Linq using Select and an Indexer

Question

I have the following query that runs successfully in LinqPad:

    var results = 
    from container in Container
    join containerType in ContainerType on container.ContainerType equals containerType
    where containerType.ContainerTypeID == 2
    select new { ContainerID = container.ContainerID, TypeID = container.ContainerTypeID};

results.Dump();

I would like to change the select to use an indexer so that the select would look something like this:

select new { ContainerID = container.ContainerID, TypeID = container.ContainerTypeID, ContainerIndex = index  };

What I cannot seem to get right is the proper syntax for select to use the select indexer.

Thanks for your help.

Answer 1

You can't get the index with the query expression format, but there's an overload for Select that you can use in dot notation that will do it. You can stick to query expression format for the bulk of it, and then add the index in an extra select projection:

var tmp = 
    from container in Container
    join containerType in ContainerType
      on container.ContainerType equals containerType
    where containerType.ContainerTypeID == 2
    select new { ContainerID = container.ContainerID,
                 TypeID = container.ContainerTypeID};

var results = tmp.Select((x, index) => new { x.ContainerID, x.TypeID, 
                                             ContainerIndex = index });

Answer 2

I'm probably missing something, but if your items in Container already have property ContainerTypeID, I don't understand why you need the join. It appears to me that joining to ContainerType is not providing any extra properties that are required for this operation.

As such:

Container
    .Where(c => c.ContainerTypeID==2)
    .Select((c,i) => new {c.ContainerID, c.TypeID, Index = i})