本文介绍了NET Core和EF Core的谓词构建的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

一个非常简单的问题:

我正在尝试创建这样的谓词构建器:

I'm trying to create a predicate builder like this :

    var predicate = PredicateBuilder.False<MyObject>();

但是 Net Core EF Core 中似乎不可用.

我是否缺少包裹或其他物品?

Am I missing a package or something ?

推荐答案

您确定使用的PredicateBuilder不是自定义类吗? PredicateBuilder作为 LINQKit 的一部分提供,但来源也可在此处获得,如下所示:

Are you sure that the PredicateBuilder you were using was not a custom class? A PredicateBuilder is shipped as part of LINQKit but the source is also available here as follows:

public static class PredicateBuilder
{
    public static Expression<Func<T, bool>> True<T>() { return f => true; }

    public static Expression<Func<T, bool>> False<T>() { return f => false; }

    public static Expression<Func<T, bool>> Or<T> (this Expression<Func<T, bool>> expr1,
                                                      Expression<Func<T, bool>> expr2)
    {
        var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast<Expression> ());
        return Expression.Lambda<Func<T, bool>>
          (Expression.OrElse (expr1.Body, invokedExpr), expr1.Parameters);
    }

    public static Expression<Func<T, bool>> And<T> (this Expression<Func<T, bool>> expr1,
                                                       Expression<Func<T, bool>> expr2)
    {
        var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast<Expression> ());
        return Expression.Lambda<Func<T, bool>>
          (Expression.AndAlso (expr1.Body, invokedExpr), expr1.Parameters);
    }
}

这篇关于NET Core和EF Core的谓词构建的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!

08-24 06:54