How to pass classProperty to LINQ using Expressions

user_17051975 0
Viewed 75

I have a LINQ query, and I want to pass Person parameters to it. Probably it should be something like this.

Expression<Func<Person, long>> exp1 = person.CarId;
Expression<Func<Person, long>> exp2 = person.PetId;

var result = db.people.Select(x => new {PersonName = x.Name, EntityId = exp1}).ToList()

How can I do it?

expression-trees entity-framework c#
2 Answers

I've used IQueryble to reuse parts of queries. It was something like the following:

var withPets = Get(GetWithPetId);
                
List<WithEntityId> Get(Func<IQueryable<Person>, IQueryable<WithEntityId>> transformer)
{
    transformer(db.People.Where(...))
        .Where( x => x.EntityId > 100)
        .ToList(); 
}

IQueryable<WithEntityId> GetWithPetId(IQueryable<Person> people)
    => people.Select(x => new WithEntityId(x.Name, x.PetId));

IQueryable<WithEntityId> GetWithCard(IQueryable<Person> people)
    => people.Select(x => new WithEntityId(x.Name, x.CarId));
user_5810760

Vanilla EF do not allow such queries. I would suggest to use LINQKit. It needs just configuring DbContextOptions:

builder
    .UseSqlServer(connectionString)
    .WithExpressionExpanding(); // enabling LINQKit extension

Then you can use your expressions in the following way:

var result = db.people
   .Select(x => new {PersonName = x.Name, EntityId = exp1.Invoke(x)})
   .ToList()
user_106463160
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