Allow select_merge in item_query (index)

[krns]

Allow select_merge in item_query when live_action is :index.

Before this change you cannot use select_merge on index because it collides with the count query for the pagination and results in the following error:

the following exception happened when compiling a subquery.

    ** (Ecto.QueryError) atoms, structs, maps, lists, tuples and sources are not allowed as map values in subquery, got: `%{child_count: {:subquery, 0}}` in query:
    
    from v0 in MyApp.Parent,
      as: :parent,
      select: merge(v0, %{
      child_count:
        subquery(
          #Ecto.Query<from a0 in MyApp.Child, where: a0.parent_id == parent_as(:parent).id, select: %{result: count()}>
        )
    })
    

The subquery originated from the following query:

from v0 in subquery(from v0 in MyApp.Parent,
  as: :parent,
  select: merge(v0, %{
  child_count:
    subquery(
      #Ecto.Query<from a0 in MyApp.Child, where: a0.parent_id == parent_as(:parent).id, select: count()>
    )
})),
  select: count()

[krns]

@pehbehbeh @Flo0807 this fixes the issue I told you a few weeks ago

[Flo0807]

@pehbehbeh @Flo0807 this fixes the issue I told you a few weeks ago

👍 Looks like an easy fix, and we don't need select queries in the count query anyway, I guess.

[krns]

Yes, the only needed select statement comes from the Repo.aggregate call.