Entity Framework Code First IQueryable

Question

I am using Entity Framework Code First and ran into a small road block. I have a class "Person" defined as such:

public class Person
{
    public Guid Id { get; set; }
    public virtual ICollection<History> History { get; set; }
}

and a class "History" defined as such:

public class History
{
    public Guid Id { get; set; }
    public virtual Person Owner { get; set; }
    public DateTime OnDate { get; set; }
}

However, when I call:

IEnumerable<History> results = person.History
                               .OrderBy(h => h.OnDate)
                               .Take(50)
                               .ToArray();

It appears to pull all of the history for the person, then order it and such in memory. Any recommendations on what I'm missing?

Thanks in advance!

Answer 1

Because you are querying an IEnumerable (ie: LINQ to Objects) not IQueryable (ie: LINQ to Entities) given by EF.

Instead you should use

IEnumerable<History> results = context.History.Where(h => h.Person.Id = "sfssd").OrderBy(h => h.OnDate).Take(50)

Answer 2

This question and the accepted answer are both a bit old. Code like this would, as the original question points, load the entire history for the person from the database - not good!

var results = person
    .History
    .OrderBy(h => h.OnDate)
    .Take(50)
    .ToArray();

With EF 6 there is an easy solution. Without rearranging your query, you can have it work the IQueryable way by making use of the DbContext.Entry method , the DbEntryEntity.Collection method , and the DbCollectionEntry.Query method .

var results = dbContext
    .Entry(person)
    .Collection(p => p.History)
    .Query()
    .OrderBy(h => h.OnDate)
    .Take(50)
    .ToArray();