CODEWITHSUNDEEP
expressionequalitylambda
theSpyCry
theSpyCry

Reputation: 12283

Linq Expression comparing property and an integer

I am trying to compare if a property of an object has the value of int. How to achieve it, please?

int id = 123;
// Func<MyClass, bool> f = x => x.A.B.Id == id;
var a = System.Linq.Expressions.MemberExpression.Property(param, "A");
var b = System.Linq.Expressions.MemberExpression.Property(a, "B");                   

body = System.Linq.Expressions.Expression.Equal(
    System.Linq.Expressions.MemberExpression.Property(b, "Id"),
    System.Linq.Expressions.MemberExpression.Constant(id, typeof(int))
);

This throws invalidoperation exception.

Upvotes: 0

Views: 1162

Answers (2)

Jon Skeet
Jon Skeet

Reputation: 1501163

It's not clear what you're doing wrong, because you haven't shown enough of your code or enough of the error. The general approach is fine. Here's a short but complete example:

using System;
using System.Linq.Expressions;

public class House
{
    public Person Owner { get; set; }
}

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

class Test
{
    static void Main()
    {
        int targetLength = 3;
        var param = Expression.Parameter(typeof(House), "p");
        var a = Expression.Property(param, "Owner");
        var b = Expression.Property(a, "Name");
        var length = Expression.Property(b, "Length");

        var target = Expression.Constant(targetLength, typeof(int));

        var body = Expression.Equal(length, target);
        var lambda = Expression.Lambda<Func<House, bool>>(body, param);

        var compiled = lambda.Compile();
        var house = new House { Owner = new Person { Name = "Jon" } };
        Console.WriteLine(compiled(house));
        house.Owner.Name = "Holly";
        Console.WriteLine(compiled(house));
    }
}

I suggest you look at the difference between my code and your code to work out what's wrong.

Upvotes: 1

theSpyCry
theSpyCry

Reputation: 12283

I found it out. The propert ID was not Int32, it was Int16. My fault. For the others. Check the object property type 3-times before you leave :)

Upvotes: 0

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