How to use Where condition inside Include in entity framework LINQ? - entity-framework

Question

My sample code lines are,
var question = context.EXTests
.Include(i => i.EXTestSections.Where(t => t.Status != (int)Status.InActive))
.Include(i => i.EXTestQuestions)
.FirstOrDefault(p => p.Id == testId);
Here Include was not supporting Where Clause. How can I modify above code?

Answer 1

You have a sequence of ExTests. Every ExText has zero or more ExTestSections, Every Extest also has a property ExtestQuestions, which is probably also a sequence. Finally every ExTest is identified by an Id.
You want a query where you get the first ExTest that has Id equal to testId, inclusive all its ExTestQuestions and some ExTestSections. You want only those ExTestSections whith an InActive status.
Use Select instead of Using
One of the slower parts of database queries is the transfer of the data from the DBMS to your process. Hence it is wise to limit it to only the data you actually plan to use.
It seems that you have designed a one-to-many relation between ExTests and its ExTestSections: every ExTest has zero or more ExTestSections and every ExTestSection belongs to exactly one ExTest. In databases this is done by giving the ExTestSection a foreign key to the ExTest that it belongs to. It might be that you've designed a many-to-many relation. The principle remains the same.
If you ask an ExTest with its hundred ExTestSections, you get the Id of the the ExTest and hundred times the value of the foreign key of the ExTestSection, thus sending the same value 101 times. What a waste.
So if you query data from the database, only query for the data you actually plan to use.
Use Include if you plan to update the queried data, otherwise use Select
Back to your question
var result = myDbContext.EXTests
.Where(exTest => exTest.Id == testId)
.Select( exTest => new
{
// only select the properties you plan to use
Id = exTest.Id;
Name = exTest.Name,
Result = exText.Result,
... // other properties
ExTestSections = exTest.Sections
.Where(exTestSection => exTestSection.Status != (int)Status.InActive)
.Select(exTestSection => new
{
// again: select only those properties you actually plan to use
Id = exTestSection.Id,
// foreign key not needed, you know it equals ExTest primary key
// ExTestId = exTestSection.ExtTestId
... // other ExtestSection properties you plan to use
})
.ToList(),
ExTestQuestions = exTest.ExTestQuestions
.Select( ...) // only the properties you'll use
})
.FirstOrDefault();
I've transferred the test on equal TestId to a Where. This would allow you to omit the Id of the requested item: you know it will equal testId, so not meaningful to transfer it.