CODEWITHSUNDEEP
c#linqicollection
szkut
szkut

Reputation: 381

IQueryable vs ICollection (List)

I have such a case study:

ToList() case:

    List<CategoryType> categories = (from c in categoryTypes where c.IsSysParam == isSysParamCategory select new CategoryType { Code = c.Code, CreateDate = c.CreateDate, EditDate = c.EditDate, IsProductCategory = c.IsProductCategory, IsSysParam = c.IsSysParam, Name = c.Name, TypeId = c.TypeId, ValueTypes = new List<ValueType>() }).ToList();

    List<ValueType> valueTypeList = new List<ValueType>();
    foreach (var c in categories.ToList())
    {
        valueTypeList = categoryTypes.Where(x => x.TypeId == c.TypeId).SelectMany(v => v.ValueTypes).Where(v => v.ParentValueId == null).ToList();
        c.ValueTypes = valueTypeList;
    }

enter image description here

IQueryable case:

When I change in first query - List<CategoryType> to IQueryable<CategoryType> and remove ToList() from the end of query then I dont have any result:

enter image description here

Question:

I am asking for an explanation, I do not understand why this is happening. I know that the IQueryable makes some part of the work on the database side.

Edit: The code is working, pictures shows the final effect.

I have:

  public IQueryable<CategoryType> CategoryTypePagination { get; set; }

and in the end of ToList() case:

this.CategoryTypePagination = categories.AsQueryable();

in IQueryable case just removed .AsQueryable()

Upvotes: 0

Views: 257

Answers (2)

Michał Turczyn
Michał Turczyn

Reputation: 37337

Accrodingly to this, IQueryable uses something called lazy loading.

So the results of IQueryable aren't loaded until they are first used, for example in Sum, ToList or ToArray methods, while ToList requieres data to be loaded. Thus you see the difference after initailizing both objects.

Upvotes: 0

Bianca
Bianca

Reputation: 382

You have to look at "Deferred Query Execution" and "Immediate Query Execution"

Upvotes: 1

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