Combine / Merge IQueryable or converting Queryover to IQueryable

[jmer...@gmail.com]

Hi all,

is there a possibility to combine several IQueryable without execute the query?

Pseudocode:

var q1 = (IQueryable<Person>).....;
var q2 = (IQueryable<Person>).....;

var q = q1.Union(q2);

or

SELECT *

FROM Table1

WHERE id IN

  (Result ids of IQueryable1)

OR

  (Result ids of IQueryable2)

I achieved a solution by using Disjunction of Queryover. As result I need an IQueryable without the query has been executed. So a solution can also be if it is possible to convert IQueryover to IQueryable.

Thanks in advance

[Oskar Berggren]

var q1 = from p in Person

            where whatever

            select p.id;

var q2 = from p in Person

            where whatever

            select p.id;

var qC = from p in Person

            where q1.Contains(p.id) || q2.Contains(p.id)

            select p;

q1 and q2 will be used as subqueries when the SQL is formed.

/Oskar

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[jmer...@gmail.com]

Hi Oskar,

thanks for your response. Sorry, I forgot one thing to mention.

In the part of code where I need to combine the IQueryable I have got some external objects in a list which provide methods which return the IQueryable to combine.

So I have s.th. like this:

foreach(var subquery in listOfIQueryablePerson)

{

  combinedIQueryable = from p allPersons

                                    where subquery.Contains(p.id) || combinedIQueryable.Contains(p.id);

}

The code above fits my requirements but it is not very nice and hasn't a good performance. Is there any other solution for that?

Thanks

[Gunnar Liljas]

You could use a PredicateBuilder (LinqKit)

var predicate=PredicateBuilder.False<Person>();

foreach(var subquery in listOfIQueryablePerson)

{

  predicate = predicate.Or(p=>subquery.Contains(p.id))

}

var combinedIQueryable = allPersons.Where(predicate);

[jmer...@gmail.com]

Thank you Gunnar. That's a good idea. There is only one thing which does not work yet. The two (or more) IQueryable are not combined via "OR" but via "AND"

Now:

SELECT *

FROM bla as b

WHERE b.Value = 20

       and (1 /* @p3 */ = 1

             or b.Id in (SELECT ....)

But it should:

SELECT *

FROM bla as b

WHERE b.Value = 20

       OR (1 /* @p3 */ = 1

             or b.Id in (SELECT ....)

This condition is created by PredicateBuilder.True<Class>() 

1 /* @p3 */ = 1

Code:

var predicate = PredicateBuilder.True<Class>();

predicate = predicate.Or(p => object.ExtendQuery().Select(x => x.Id).Contains(p.Id));

var combinedIQueryable = allUserNotes.Where(predicate);

[Gunnar Liljas]

But is that all? In your previous example you hade multiple expressions in listOfIQueryablePerson. If that's not the case, a predicate builder may be unnecessary.

You can't use  PredicateBuilder.True<Class>() and predicate.Or, since if you do the expression will always evaluate to true. Use  PredicateBuilder.False<Class>();

/G

[Oskar Berggren]

He means the AND versus OR immediately after "b.Value = 20" - since the LINQ for that isn't shown I assume it was inserted in the allUserNotes query earlier with a different Where() call. There is always AND between all Where()-calls.

/Oskar

[Gunnar Liljas]

Ok, but this predicate

var predicate = PredicateBuilder.True<Class>();

predicate = predicate.Or(p => object.ExtendQuery().Select(x => x.Id).Contains(p.Id));

var combinedIQueryable = allUserNotes.Where(predicate);

will always evaluate to true

[Oskar Berggren]

Yes, there is two remaining problems.

/Oskar