在我的winform应用程序中,我使用以下代码来查找用户:
var findUser =
userService.Find(
u => u.UserName == UserNameTextBox.Text.Trim() && u.Password == PasswordTextBox.Text.Trim() && u.IsActive);
并在我的服务层中查找实现为通用方法的方法:
public virtual TEntity Find(Func<TEntity, bool> predicate)
{
return _tEntities.Where(predicate).FirstOrDefault();
}
当我执行此操作时,以下sql代码生成并发送到sql server:
SELECT
[Extent1].[Id] AS [Id],
[Extent1].[FirstName] AS [FirstName],
[Extent1].[LastName] AS [LastName],
[Extent1].[UserName] AS [UserName],
[Extent1].[Password] AS [Password],
[Extent1].[IsAdmin] AS [IsAdmin],
[Extent1].[IsActive] AS [IsActive],
[Extent1].[RowVersion] AS [RowVersion]
FROM [dbo].[Users] AS [Extent1]
问题出在哪里?如何修复主题?
Where
函数在多个类型上定义了多个重载作为扩展方法。
使用Func<TEntity, bool> predicate
,您调用的是Enumerable.Where
,它在客户端评估您的筛选,这就是为什么它不能生成正确的查询。
您需要的是接受Expression<Func<TSource, bool>> predicate
的Queryable.Where
方法
因此,将Find
方法签名更改为:
public virtual TEntity Find(Expression<Func<TEntity, bool>> predicate)
{
return _tEntities.Where(predicate).FirstOrDefault();
}