CODEWITHSUNDEEP
c#asp.net-coreexpression
Sándor Hatvani
Sándor Hatvani

Reputation: 465

Dynamically created expression

I try to creat an expression for Linq query dynamically but it gives just this message back:

{Method = Internal Error evaluating expression} I use Vs 2019 and .NET Core 3.1. class Client { public string Name { get; set; } ... }

        var parameter = Expression.Parameter(typeof(Client), "x");
        var member = Expression.Property(parameter, "Name");
        var constant = Expression.Constant("X Y");
        var exp = Expression.Equal(member, constant);
        var func = Expression.Lambda(exp, parameter).Compile();

Where do I make a mistake, please?

UPDATE

namespace Domain
{
public class Client
{
    public string Name { get; set; }

    public string UserName { get; set; }

    public string Department { get; set; }

    public string CompanyPhoneNumber { get; set; }

    public string PrivateMobileNumber { get; set; }

    public string ComputerName { get; set; }

    public Guid InternetProviderId { get; set; }

    public virtual InternetProvider InternetProvider { get; set; }

    public string OtherInternetProvider { get; set; }
}
}

Upvotes: 0

Views: 408

Answers (1)

Martin Staufcik
Martin Staufcik

Reputation: 9490

Expression.Lambda method has a generic version that allows to specify the delegate type, the last line can be modified to:

var func = Expression.Lambda<Func<Client, bool>>(exp, parameter).Compile();

Example of use:

var list = new List<Client>
{
    new Client() { Name = "X Y"}
};

var l2 = list.Where(func).ToList();

Working example: here.

Upvotes: 1

Related Questions