Entity Framework 第四篇优化SQL查询

mac2022-06-30 32

Expression<Func<TEntity, bool>>与Func<TEntity, bool>的异同 public IList<TEntity> Search<TEntity>(Expression<Func<TEntity, bool>> predicate = null) where TEntity : class { if (predicate == null) { return dbContext.Set<TEntity>().ToList(); } else { return dbContext.Set<TEntity>().Where(predicate).ToList(); } }

本人通过跟踪sql语句得知

predicate如果为委托类型的时候，dbContext.Set<TEntity>().Where(predicate).ToList();对应的sql语句是

SELECT [Extent1].[UserID] AS [UserID], [Extent1].[LoginName] AS [LoginName], [Extent1].[Password] AS [Password], [Extent1].[UserName] AS [UserName], [Extent1].[UserType] AS [UserType], [Extent1].[Tel] AS [Tel], [Extent1].[CreateDate] AS [CreateDate], [Extent1].[LoginNum] AS [LoginNum], [Extent1].[LastDate] AS [LastDate], [Extent1].[ShopID] AS [ShopID] FROM [dbo].[S_Users] AS [Extent1]

但是当predicate如果为表达式树的时候，语句如下，

所以我们尽量用表达式树传参，而不是单纯地lambda表达式或者委托类型。

为什么会这样呢？

因为dbContext.Set<TEntity>().Where(predicate)，当是表达式树的时候返回的是IQueryable<TSource>

public static IQueryable<TSource> Where<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate);

如果是委托类型返回的是IEnumerable<TSource>public static IEnumerable<TSource> Where<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate);

转载于:https://www.cnblogs.com/njcxwz/p/5581388.html

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Entity Framework 第四篇 优化SQL查询

Entity Framework 第四篇优化SQL查询