NET Core和EF Core的谓词构建 [英] Predicate build with NET Core and EF Core

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 和 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

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);
    }
}

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