数据库
我们先在SQL Server数据库中建立一个Book表：
CREATE TABLE [dbo].[Book]([ID] [int] IDENTITY(1,1) NOT NULL,[BookName] [nvarchar](50) NULL,[BookDescription] [nvarchar](50) NULL,[ISBN] [nvarchar](20) NULL,[CreateTime] [datetime] NULL,CONSTRAINT [PK_Book] PRIMARY KEY CLUSTERED ([ID] ASC)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]) ON [PRIMARY]GOALTER TABLE [dbo].[Book] ADD CONSTRAINT [DF_Book_CreateTime] DEFAULT (getdate()) FOR [CreateTime]GO
然后插入如下数据：
INSERT [dbo].[Book] ([BookName], [BookDescription], [ISBN]) VALUES (N'Chinese', N'Chinese', N'0001')GOINSERT [dbo].[Book] ([BookName], [BookDescription], [ISBN]) VALUES (N'English', N'English', N'0002')GOINSERT [dbo].[Book] ([BookName], [BookDescription], [ISBN]) VALUES (N'Japanese', N'Japanese', N'0003')GOINSERT [dbo].[Book] ([BookName], [BookDescription], [ISBN]) VALUES (N'Russian', N'Russian', N'0004')GOINSERT [dbo].[Book] ([BookName], [BookDescription], [ISBN]) VALUES (N'Italian', N'Italian', N'0005')GO
查询Book表的数据，如下图所示：
现在我们使用EF Core将Book表映射到.NET Core控制台项目中的Book实体上，Book实体如下所示：
using System;using System.Collections.Generic;namespace EFCoreDB.Entities{public partial class Book{public int Id { get; set; }public string BookName { get; set; }public string BookDescription { get; set; }public string Isbn { get; set; }public DateTime? CreateTime { get; set; }}}
不使用事务
然后我们在.NET Core控制台项目Program类的Main方法中，使用DbContext（也就是FinanceDigitalToolContext）读取BookName为"Chinese"的Book实体，然后使用DbContext.SaveChanges方法两次更改其BookDescription属性的值，再从数据库中将其查询出来显示，代码如下：
using EFCoreDB.Entities;using System;using System.Linq;using System.Linq.Expressions;namespace EFCoreDB{class Program{static void Main(string[] args){using (FinanceDigitalToolContext dbContext = new FinanceDigitalToolContext()){Expression<Func<Book, bool>> bookExpression = b => b.BookName == "Chinese";//构造查询条件，来查询BookName为Chinese的Bookvar chineseBook = dbContext.Book.First(bookExpression);//获取BookName为Chinese的Book实体chineseBookchineseBook.BookDescription = "This is a Chinese book";//更改chineseBook的BookDescription属性dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库chineseBook.BookDescription = "This is a very good Chinese book";//再次更改chineseBook的BookDescription属性dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库chineseBook = dbContext.Book.First(bookExpression);//重新获取BookName为Chinese的Book实体chineseBook//显示当前chineseBook的当前BookDescription属性值Console.WriteLine(chineseBook.BookName + " book has description: \"" + chineseBook.BookDescription + "\"");}Console.WriteLine("Press key to quit....");Console.ReadLine();}}}
执行上面的代码，我们使用EF Core的日志功能，输出每次DbContext访问数据库时的后台日志信息：
首先在执行
var chineseBook = dbContext.Book.First(bookExpression);//获取BookName为Chinese的Book实体chineseBook
时，EF Core的日志如下所示：
=============================== EF Core log started ===============================Opening connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Opened connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Executing DbCommand [Parameters=[], CommandType='Text', CommandTimeout='30']SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]FROM [Book] AS [b]WHERE [b].[BookName] = N'Chinese'=============================== EF Core log finished ============================================================== EF Core log started ===============================Executed DbCommand (129ms) [Parameters=[], CommandType='Text', CommandTimeout='30']SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]FROM [Book] AS [b]WHERE [b].[BookName] = N'Chinese'=============================== EF Core log finished ============================================================== EF Core log started ===============================A data reader was disposed.=============================== EF Core log finished ============================================================== EF Core log started ===============================Closing connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Closed connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Context 'Book' started tracking 'FinanceDigitalToolContext' entity. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values.=============================== EF Core log finished ===============================
从日志中我们可以看出来，dbContext.Book.First(bookExpression)在数据库中开启了一个数据库连接，并使用SQL语句做了查询，然后关闭了数据库连接。
然后在执行下面的代码
chineseBook.BookDescription = "This is a Chinese book";//更改chineseBook的BookDescription属性dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库
时，EF Core的日志如下所示：
=============================== EF Core log started ===============================SaveChanges starting for 'FinanceDigitalToolContext'.=============================== EF Core log finished ============================================================== EF Core log started ===============================DetectChanges starting for 'FinanceDigitalToolContext'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Unchanged 'Book.BookDescription' detected as changed and will be marked as modified. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see property values.=============================== EF Core log finished ============================================================== EF Core log started ===============================An 'Book' entity tracked by 'FinanceDigitalToolContext' changed from 'Unchanged' to 'Modified'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values.=============================== EF Core log finished ============================================================== EF Core log started ===============================DetectChanges completed for 'FinanceDigitalToolContext'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Opening connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Opened connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Beginning transaction with isolation level 'ReadCommitted'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Executing DbCommand [Parameters=[@p1='?' (DbType = Int32), @p0='?' (Size = 50)], CommandType='Text', CommandTimeout='30']SET NOCOUNT ON;UPDATE [Book] SET [BookDescription] = @p0WHERE [ID] = @p1;SELECT @@ROWCOUNT;=============================== EF Core log finished ============================================================== EF Core log started ===============================Executed DbCommand (86ms) [Parameters=[@p1='?' (DbType = Int32), @p0='?' (Size = 50)], CommandType='Text', CommandTimeout='30']SET NOCOUNT ON;UPDATE [Book] SET [BookDescription] = @p0WHERE [ID] = @p1;SELECT @@ROWCOUNT;=============================== EF Core log finished ============================================================== EF Core log started ===============================A data reader was disposed.=============================== EF Core log finished ============================================================== EF Core log started ===============================Committing transaction.=============================== EF Core log finished ============================================================== EF Core log started ===============================Closing connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Closed connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Disposing transaction.=============================== EF Core log finished ============================================================== EF Core log started ===============================An 'Book' entity tracked by 'FinanceDigitalToolContext' changed from 'Modified' to 'Unchanged'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values.=============================== EF Core log finished ============================================================== EF Core log started ===============================SaveChanges completed for 'FinanceDigitalToolContext' with 1 entities written to the database.=============================== EF Core log finished ===============================
从日志中我们可以看出来在执行dbContext.SaveChanges方法时，EF Core在数据库中开启了一个数据库连接，并使用SQL语句做了数据库更改，然后关闭了数据库连接。然后chineseBook这个Book实体的EntityState从Modified变为了Unchanged。
然后执行代码
chineseBook.BookDescription = "This is a very good Chinese book";//再次更改chineseBook的BookDescription属性dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库
时，EF Core的日志如下所示：
=============================== EF Core log started ===============================SaveChanges starting for 'FinanceDigitalToolContext'.=============================== EF Core log finished ============================================================== EF Core log started ===============================DetectChanges starting for 'FinanceDigitalToolContext'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Unchanged 'Book.BookDescription' detected as changed and will be marked as modified. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see property values.=============================== EF Core log finished ============================================================== EF Core log started ===============================An 'Book' entity tracked by 'FinanceDigitalToolContext' changed from 'Unchanged' to 'Modified'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values.=============================== EF Core log finished ============================================================== EF Core log started ===============================DetectChanges completed for 'FinanceDigitalToolContext'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Opening connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Opened connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Beginning transaction with isolation level 'ReadCommitted'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Executing DbCommand [Parameters=[@p1='?' (DbType = Int32), @p0='?' (Size = 50)], CommandType='Text', CommandTimeout='30']SET NOCOUNT ON;UPDATE [Book] SET [BookDescription] = @p0WHERE [ID] = @p1;SELECT @@ROWCOUNT;=============================== EF Core log finished ============================================================== EF Core log started ===============================Executed DbCommand (19ms) [Parameters=[@p1='?' (DbType = Int32), @p0='?' (Size = 50)], CommandType='Text', CommandTimeout='30']SET NOCOUNT ON;UPDATE [Book] SET [BookDescription] = @p0WHERE [ID] = @p1;SELECT @@ROWCOUNT;=============================== EF Core log finished ============================================================== EF Core log started ===============================A data reader was disposed.=============================== EF Core log finished ============================================================== EF Core log started ===============================Committing transaction.=============================== EF Core log finished ============================================================== EF Core log started ===============================Closing connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Closed connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Disposing transaction.=============================== EF Core log finished ============================================================== EF Core log started ===============================An 'Book' entity tracked by 'FinanceDigitalToolContext' changed from 'Modified' to 'Unchanged'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values.=============================== EF Core log finished ============================================================== EF Core log started ===============================SaveChanges completed for 'FinanceDigitalToolContext' with 1 entities written to the database.=============================== EF Core log finished ===============================
同样从日志中我们可以看出来在执行dbContext.SaveChanges方法时，EF Core在数据库中开启了一个数据库连接，并使用SQL语句做了数据库更改，然后关闭了数据库连接。然后chineseBook这个Book实体的EntityState从Modified变为了Unchanged。
然后执行代码
chineseBook = dbContext.Book.First(bookExpression);//重新获取BookName为Chinese的Book实体chineseBook
时，EF Core的日志如下所示：
=============================== EF Core log started ===============================Opening connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Opened connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Executing DbCommand [Parameters=[], CommandType='Text', CommandTimeout='30']SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]FROM [Book] AS [b]WHERE [b].[BookName] = N'Chinese'=============================== EF Core log finished ============================================================== EF Core log started ===============================Executed DbCommand (21ms) [Parameters=[], CommandType='Text', CommandTimeout='30']SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]FROM [Book] AS [b]WHERE [b].[BookName] = N'Chinese'=============================== EF Core log finished ============================================================== EF Core log started ===============================A data reader was disposed.=============================== EF Core log finished ============================================================== EF Core log started ===============================Closing connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Closed connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ===============================
从日志中我们可以看出来，dbContext.Book.First(bookExpression)在数据库中还是开启了一个数据库连接，并使用SQL语句做了查询，然后关闭了数据库连接。
总结下来，上面的代码和日志发生的事情如下：
dbContext.Book.First(bookExpression)开启和关闭了一个数据库连接，查询BookName为Chinese的Book实体chineseBook第一个dbContext.SaveChanges()开启和关闭了一个数据库连接，更改chineseBook的BookDescription属性值"This is a Chinese book"到数据库第二个dbContext.SaveChanges()开启和关闭了一个数据库连接，更改chineseBook的BookDescription属性值"This is a very good Chinese book"到数据库dbContext.Book.First(bookExpression)开启和关闭了一个数据库连接，重新查询BookName为Chinese的Book实体chineseBook
所以综上所述DbContext一共开启了和关闭了四个数据库连接。
使用事务
现在我们更改Program类Main方法中的代码，将两次DbContext.SaveChanges方法的调用都放在一个TransactionScope事务范围中，所以现在两次DbContext.SaveChanges方法提交的SQL都会在同一个数据库事务中，代码如下所示：
using EFCoreDB.Entities;using System;using System.Linq;using System.Linq.Expressions;using System.Transactions;namespace EFCoreDB{class Program{static void Main(string[] args){using (FinanceDigitalToolContext dbContext = new FinanceDigitalToolContext()){Expression<Func<Book, bool>> bookExpression = b => b.BookName == "Chinese";//构造查询条件，来查询BookName为Chinese的Bookvar chineseBook = dbContext.Book.First(bookExpression);//获取BookName为Chinese的Book实体chineseBook//使用TransactionScope事务范围来开启一个数据库事务using (TransactionScope transactionScope = new TransactionScope(TransactionScopeOption.RequiresNew)){chineseBook.BookDescription = "This is a Chinese book";//更改chineseBook的BookDescription属性dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库，由于TransactionScope事务范围的存在，所以DbContext.SaveChanges方法提交的SQL语句都存在于TransactionScope的事务当中chineseBook.BookDescription = "This is a very good Chinese book";//再次更改chineseBook的BookDescription属性dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库，由于TransactionScope事务范围的存在，所以DbContext.SaveChanges方法提交的SQL语句都存在于TransactionScope的事务当中plete();//提交TransactionScope事务范围中的SQL语句到数据库，数据库事务结束}chineseBook = dbContext.Book.First(bookExpression);//重新获取BookName为Chinese的Book实体chineseBook//显示当前chineseBook的当前BookDescription属性值Console.WriteLine(chineseBook.BookName + " book has description: \"" + chineseBook.BookDescription + "\"");}Console.WriteLine("Press key to quit....");Console.ReadLine();}}}
执行上面的代码，我们还是使用EF Core的日志功能，输出每次DbContext访问数据库时的后台日志信息：
首先执行
var chineseBook = dbContext.Book.First(bookExpression);//获取BookName为Chinese的Book实体chineseBook
时，EF Core的日志如下所示：
=============================== EF Core log started ===============================Opening connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Opened connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Executing DbCommand [Parameters=[], CommandType='Text', CommandTimeout='30']SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]FROM [Book] AS [b]WHERE [b].[BookName] = N'Chinese'=============================== EF Core log finished ============================================================== EF Core log started ===============================Executed DbCommand (139ms) [Parameters=[], CommandType='Text', CommandTimeout='30']SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]FROM [Book] AS [b]WHERE [b].[BookName] = N'Chinese'=============================== EF Core log finished ============================================================== EF Core log started ===============================A data reader was disposed.=============================== EF Core log finished ============================================================== EF Core log started ===============================Closing connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Closed connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Context 'Book' started tracking 'FinanceDigitalToolContext' entity. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values.=============================== EF Core log finished ===============================
从日志中我们可以看出来，dbContext.Book.First(bookExpression)在数据库中开启了一个数据库连接，并使用SQL语句做了查询，然后关闭了数据库连接。
然后执行
using (TransactionScope transactionScope = new TransactionScope(TransactionScopeOption.RequiresNew)){
TransactionScope的事务范围开始，此时数据库事务已经开始，EF Core没有输出日志
然后执行
chineseBook.BookDescription = "This is a Chinese book";//更改chineseBook的BookDescription属性dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库，由于TransactionScope事务范围的存在，所以DbContext.SaveChanges方法提交的SQL语句都存在于TransactionScope的事务当中
时，EF Core的日志如下所示：
=============================== EF Core log started ===============================SaveChanges starting for 'FinanceDigitalToolContext'.=============================== EF Core log finished ============================================================== EF Core log started ===============================DetectChanges starting for 'FinanceDigitalToolContext'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Unchanged 'Book.BookDescription' detected as changed and will be marked as modified. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see property values.=============================== EF Core log finished ============================================================== EF Core log started ===============================An 'Book' entity tracked by 'FinanceDigitalToolContext' changed from 'Unchanged' to 'Modified'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values.=============================== EF Core log finished ============================================================== EF Core log started ===============================DetectChanges completed for 'FinanceDigitalToolContext'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Opening connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Opened connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Enlisted in an ambient transaction with isolation level 'Serializable'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Executing DbCommand [Parameters=[@p1='?' (DbType = Int32), @p0='?' (Size = 50)], CommandType='Text', CommandTimeout='30']SET NOCOUNT ON;UPDATE [Book] SET [BookDescription] = @p0WHERE [ID] = @p1;SELECT @@ROWCOUNT;=============================== EF Core log finished ============================================================== EF Core log started ===============================Executed DbCommand (79ms) [Parameters=[@p1='?' (DbType = Int32), @p0='?' (Size = 50)], CommandType='Text', CommandTimeout='30']SET NOCOUNT ON;UPDATE [Book] SET [BookDescription] = @p0WHERE [ID] = @p1;SELECT @@ROWCOUNT;=============================== EF Core log finished ============================================================== EF Core log started ===============================A data reader was disposed.=============================== EF Core log finished ============================================================== EF Core log started ===============================An 'Book' entity tracked by 'FinanceDigitalToolContext' changed from 'Modified' to 'Unchanged'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values.=============================== EF Core log finished ============================================================== EF Core log started ===============================SaveChanges completed for 'FinanceDigitalToolContext' with 1 entities written to the database.=============================== EF Core log finished ===============================
从日志中我们可以看出来在执行dbContext.SaveChanges方法时，EF Core在数据库中开启了一个数据库连接，并使用SQL语句做了数据库更改，但是没有关闭数据库连接。然后chineseBook这个Book实体的EntityState从Modified变为了Unchanged。
然后执行
chineseBook.BookDescription = "This is a very good Chinese book";//再次更改chineseBook的BookDescription属性dbContext.SaveChanges();//用DbContext.SaveChanges方法保存更改到数据库，由于TransactionScope事务范围的存在，所以DbContext.SaveChanges方法提交的SQL语句都存在于TransactionScope的事务当中
时，EF Core的日志如下所示：
=============================== EF Core log started ===============================SaveChanges starting for 'FinanceDigitalToolContext'.=============================== EF Core log finished ============================================================== EF Core log started ===============================DetectChanges starting for 'FinanceDigitalToolContext'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Unchanged 'Book.BookDescription' detected as changed and will be marked as modified. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see property values.=============================== EF Core log finished ============================================================== EF Core log started ===============================An 'Book' entity tracked by 'FinanceDigitalToolContext' changed from 'Unchanged' to 'Modified'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values.=============================== EF Core log finished ============================================================== EF Core log started ===============================DetectChanges completed for 'FinanceDigitalToolContext'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Executing DbCommand [Parameters=[@p1='?' (DbType = Int32), @p0='?' (Size = 50)], CommandType='Text', CommandTimeout='30']SET NOCOUNT ON;UPDATE [Book] SET [BookDescription] = @p0WHERE [ID] = @p1;SELECT @@ROWCOUNT;=============================== EF Core log finished ============================================================== EF Core log started ===============================Executed DbCommand (22ms) [Parameters=[@p1='?' (DbType = Int32), @p0='?' (Size = 50)], CommandType='Text', CommandTimeout='30']SET NOCOUNT ON;UPDATE [Book] SET [BookDescription] = @p0WHERE [ID] = @p1;SELECT @@ROWCOUNT;=============================== EF Core log finished ============================================================== EF Core log started ===============================A data reader was disposed.=============================== EF Core log finished ============================================================== EF Core log started ===============================An 'Book' entity tracked by 'FinanceDigitalToolContext' changed from 'Modified' to 'Unchanged'. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see key values.=============================== EF Core log finished ============================================================== EF Core log started ===============================SaveChanges completed for 'FinanceDigitalToolContext' with 1 entities written to the database.=============================== EF Core log finished ===============================
从日志中我们可以看出来在执行dbContext.SaveChanges方法时，EF Core在数据库中并没有开启新的数据库连接，而是沿用了上一个DbContext.SaveChanges方法开启的数据库连接来提交SQL语句到数据库。然后chineseBook这个Book实体的EntityState从Modified变为了Unchanged。
然后执行
plete();//提交TransactionScope事务范围中的SQL语句到数据库，数据库事务结束}
提交TransactionScope的事务到数据库，此时数据库事务结束，TransactionScope的事务范围也结束，EF Core没有输出日志
然后执行
chineseBook = dbContext.Book.First(bookExpression);//重新获取BookName为Chinese的Book实体chineseBook
时，EF Core的日志如下所示：
=============================== EF Core log started ===============================Executing DbCommand [Parameters=[], CommandType='Text', CommandTimeout='30']SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]FROM [Book] AS [b]WHERE [b].[BookName] = N'Chinese'=============================== EF Core log finished ============================================================== EF Core log started ===============================Executed DbCommand (24ms) [Parameters=[], CommandType='Text', CommandTimeout='30']SELECT TOP(1) [b].[ID], [b].[BookDescription], [b].[BookName], [b].[CreateTime], [b].[ISBN]FROM [Book] AS [b]WHERE [b].[BookName] = N'Chinese'=============================== EF Core log finished ============================================================== EF Core log started ===============================A data reader was disposed.=============================== EF Core log finished ============================================================== EF Core log started ===============================Closing connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ============================================================== EF Core log started ===============================Closed connection to database 'FinanceDigitalTool' on server 'CNGDCAAITSQL01'.=============================== EF Core log finished ===============================
从日志中我们可以看出来，dbContext.Book.First(bookExpression)在数据库中也没有开启新的数据库连接，而是继续沿用了第一个DbContext.SaveChanges方法开启的数据库连接，使用SQL语句做了查询，之后关闭了第一个DbContext.SaveChanges方法开启的数据库连接，所以可以看到第一个DbContext.SaveChanges方法开启的数据库连接，现在才被关闭，这和不使用事务时是完全不一样的。
总结下来，使用事务后的代码和日志发生的事情如下：
dbContext.Book.First(bookExpression)开启和关闭了一个数据库连接，查询BookName为Chinese的Book实体chineseBookusing (TransactionScope transactionScope = new TransactionScope(TransactionScopeOption.RequiresNew)){开启了TransactionScope事务范围，数据库事务开始第一个dbContext.SaveChanges()开启一个数据库连接，但是没有关闭数据库连接，更改chineseBook的BookDescription属性值"This is a Chinese book"到数据库第二个dbContext.SaveChanges()没有开启新的数据库连接，而是沿用了上一个DbContext.SaveChanges方法开启的数据库连接，更改chineseBook的BookDescription属性值"This is a very good Chinese book"到数据库plete()提交TransactionScope事务范围的数据库事务到数据库，数据库事务结束}TransactionScope事务范围结束dbContext.Book.First(bookExpression)没有开启新的数据库连接，而是沿用了第一个DbContext.SaveChanges方法开启的数据库连接，重新查询BookName为Chinese的Book实体chineseBook，最后关闭了第一个DbContext.SaveChanges方法开启的数据库连接。
所以综上所述DbContext这次一共只开启和关闭了两个数据库连接，并且第二个数据库连接执行了三次数据库操作(两次DbContext.SaveChanges更改数据，一次Book.First查询数据)才被关闭。
由此我们可以看到EF Core在处于事务中时，会优化底层开启和关闭数据库连接的机制，因为EF Core觉得两次DbContext.SaveChanges方法提交的SQL语句既然都在同一个事务中，所以就没有必要每次都开启和关闭一个数据库连接，而是沿用了第一次DbContext.SaveChanges方法开启的数据库连接，所以这和没有使用事务的时候是完全不一样的。
