如何在多个条件下构建Lambda表达式树 [英] How Build Lambda Expression Tree with multiple conditions

问题描述

注意:我知道使用动态linq创建它非常简单，但是我想学习.

Note: I know it's much simple to create this using dynamic linq but I want to learn.

我想创建一个查找"的lambda:Name = David AND Age = 10.

I want to create a lambda that "finds": Name=David AND Age=10.

 class Person
    {
       public int Age { get; set; }
       public string Name { get; set; }
    }

    var lambda = LabmdaExpression<Person>("Name", "David", "Age", 10);

static Expression<Func<T, bool>> LabmdaExpression<T>(string property1, string value1, string property2, int value2)
{

     ParameterExpression parameterExpression = Expression.Parameter(typeof(Person), "o");
     MemberExpression memberExpression1 = Expression.PropertyOrField(parameterExpression, property1);
     MemberExpression memberExpression2 = Expression.PropertyOrField(parameterExpression, property2);

     ConstantExpression valueExpression1 = Expression.Constant(value1, typeof(string));
     ConstantExpression valueExpression2 = Expression.Constant(value2, typeof(int));

     BinaryExpression binaryExpression1 = Expression.Equal(memberExpression1, valueExpression1);
     BinaryExpression binaryExpression2 = Expression.Equal(memberExpression2, valueExpression2);

     var ret1 =   Expression.Lambda<Func<T, bool>>(binaryExpression1, parameterExpression);
     var ret2 =   Expression.Lambda<Func<T, bool>>(binaryExpression2, parameterExpression);


   }

推荐答案

Expression andExpression = Expression.AndAlso(binaryExpression1, binaryExpression2);

return Expression.Lambda<Func<T, bool>>(andExpression , parameterExpression);

编辑-评论

您只需将所有表达式链接在一起

You just chain together all your expresions

所以为了得到这个表达式 X AND(Y OR(Z OR Q))

so in order to get this expression X AND (Y OR (Z OR Q))

Expression ZorQ = Expression.OrElse(zExp, qExp);
Expression YorZorQ = Expression.OrElse(yExp, ZorQ);
Expression XandYorZorQ = Expression.AndAlso(xExp, YorZorQ);

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