Conditional eager loading?

I want to load an entity and it's children conditionally开发者_JAVA百科 (I only want to eager load the children when the child.IsActive == true). How do I perform the following?

var parent = 
    from p in db.tblParents.Include("tblChildren") <-- where tblChildren.IsActive == true
    where p.PrimaryKey == 1
    select p;

NOTE: I do not want to return an anonymous type.

Thanks.

One way for doing so is:

var parent = from p in db.tblParents where p.PrimaryKey == 1
             select new {
                 Parent = p,
                 Children = p.tblChildren.Where(c => c.IsActive == true)
             }.ToList();

However, you might not like the idea to return an anonymous type, then I would suggest to code it this way:

var parent = (from p in db.tblParents where p.PrimaryKey == 1).Single();
var childrens = ctx.Contacts.Where(c => c.ParentID == 1 && c.IsActive == true);
foreach (var child in childrens) {
   parent.tblChildren.Add(child);
}

Entity Framework 6 introduces Interception http://entityframework.codeplex.com/wikipage?title=Interception which can be used to adjust the SQL to Filter the children.

Before executing your query add an interceptor and remove when it's not relevant:

var interceptor = new ActiveTagsInterceptor();
DbInterception.Add(interceptor);

documents = context.Documents
                .AsQueryable()
                .Include(d => d.Tags)

DbInterception.Remove(interceptor);

Sample Interceptor which adds "[Active] = 1 And" when loading Tags:

public class ActiveTagsInterceptor : IDbCommandInterceptor
{
    public void NonQueryExecuting(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
    {
    }

    public void NonQueryExecuted(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
    {
    }

    public void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
    {
        // [Tag] AS [Extent6] ON   => [Tag] AS [Extent6] ON [Extent6].[Active] = 1 And 
        const string pattern = "\\[Tag\\]\\sAS\\s\\[([\\w]+)\\]\\sON";
        const string replacement = "$& [$1].[Active] = 1 And ";
        command.CommandText = Regex.Replace(command.CommandText, pattern, replacement);
    }

    public void ReaderExecuted(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
    {
    }

    public void ScalarExecuting(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
    {
    }

    public void ScalarExecuted(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
    {
    }
}

To be able to apply filter, better option is using Explicitly loading along with Query() instead of Eager loading :

var parent = db.tblParents.Find(1);
db.Entry(parent).Collection(p => p.tblChildren).Query().
    Where(child => child.IsActive).Load();

The Query method provides access to the underlying query that the Entity Framework will use when loading related entities. Also you need to turn off lazy loading for the navigation property(remove Virtual keyword) otherwise the collection gets loaded automatically by the lazy loading which ignores your filter.