如何在 C# 中创建自定义 Like 表达式？

Question

我正在创建一个字典以在我的应用程序中使用，如下所示。这是实体框架。

var expressions = new Dictionary<string, Func<Expression, Expression, Expression>>
{
    { "is equal to", Expression.Equal },
    { "greater then", Expression.GreaterThan }
};

但我需要一个 Like 表达式 "Expression.Like" 用于类似 sql 的查询。但是这个方法不存在。

Expression.Equal 定义如下：

public static BinaryExpression Equal(Expression left, Expression right)

所以我需要创建一个名为 Like 的自定义方法。我怎样才能做到这一点？我找不到。

public static BinaryExpression Like(Expression left, Expression right)
{
   ???
}

Answer 1

不确定这是否是您要查找的内容，但您可以创建一个扩展方法。

public static class MyExtensions
{
    public static BinaryExpression Like(this BinaryExpression obj, Expression left, Expression right)
    {
        //code here...
    }
}

Answer 2

你可以从 DbFunctions 得到这个，类似这样的东西

var methodInfo = typeof(DbFunctions).GetMethod(nameof(DbFunctions.Like), new Type[] { typeof(string) });

下面还有like函数的定义。会有帮助的

        //
        // Summary:
        //     When used as part of a LINQ to Entities query, this method invokes the canonical
        //     Like EDM operator to match an expression.
        //
        // Parameters:
        //   searchString:
        //     The string to search.
        //
        //   likeExpression:
        //     The expression to match against.
        //
        // Returns:
        //     True if the searched string matches the expression; otherwise false.
        //
        // Remarks:
        //     You cannot call this function directly. This function can only appear within
        //     a LINQ to Entities query. This function is translated to a corresponding function
        //     in the database.
        [SuppressMessage("Microsoft.Naming", "CA1720:IdentifiersShouldNotContainTypeNames", MessageId = "string")]
        [SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", MessageId = "searchString")]
        [SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", MessageId = "likeExpression")]
        public static bool Like(string searchString, string likeExpression);