Constucting complex viewmodel using MultiMap?

[Wayne Douglas]

Say I have the following documents in RavenDb:

public class TopLevel

{

    public string Id { get; set; }

    public string Name { get; set; } 

}

public class NextLevel

{

    public string Id { get; set; }

    public string TopLevelId { get; set; }

    public string Name { get; set; }  

}

public class Leaf

{

    public string Id { get; set; }

    public string NextLevelId { get; set; }

    public string Name { get; set; }

}

And the following viewmodels:

public class TopLevelViewModel

{

    public string Id { get; set; }

    public string Name { get; set; }

    public List<NextLeveViewModell> NextLevels { get; set; }

}

public class NextLevelViewModel

{

    public string Id { get; set; }

    public string TopLevelId { get; set; }

    public string Name { get; set; }

    public List<LeafViewModel> Leaves { get; set; }

}

public class LeafViewModel

{

    public string Id { get; set; }

    public string NextLevelId { get; set; }

    public string Name { get; set; }

}

What would be the best way of constructing that view model without making loads of trips to the db and manually collecting / constructing the structure?

Could I use multi-map for this?

Might be a dumb question but I've not used RavenDb in a while! Been doing Android / iPhone dev so a little rusty!

Thanks

W://

[Oren Eini (Ayende Rahien)]

Probably using a result transformer.

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[Wayne Douglas]

Result transformer lets me load a single document at the top level.

This needs to load a collection with a child collection.

[Oren Eini (Ayende Rahien)]

How would you load this using client code?

[Wayne Douglas]

Something horrible like 

Load all of the toplevel, nextlevel and leaf docs using 3 queries

loop through toplevels -> map to toplevelviewmodel

--get all nextlevels where toplevelid == toplevel.id -> map to toplevelviewmodel.nextlevels

--- loop thorugh all nextlevels 

--- get all leafs where nextlevelid == nextlevel.id -> map to nextlevelviewmodel.leafs

I'm wondering if maintaining a view on the server using triggers is possible? I don't like the thought of that though if i'm honest.

w

[Oren Eini (Ayende Rahien)]

There is no way to do this with the current structure.

You need to store the references to the next level at the top level.

[Wayne Douglas]

If I flip the references - what would be the best approach?

[Wayne Douglas]

Or am I barking up the wrong tree with this?

[Kijana Woodard]

You could have references both ways. Any reason why there are three explicit doc types and not one with IsTop and IsLeaf properties?

[Wayne Douglas]

They are completely unrelated objects - I've just completely simplified it here - IsLeaf has no meaning to these objects - I should have called them something else perhaps...

think of it as:

- Invoice

- - OrderLIne

- - - OrderEntry

Although this doesn't really fit the bill as each object at each level has a need for it's own ID hence they are in their own document with their own Ids - as they all will need to be loaded separately.

I just need to be able to construct them in this manner for this view model.

w

[Wayne Douglas]

I had this before by basically using CQRS and maintained the VM in the readmodel.

I'm tempted to do the same using triggers as I don't think this is possible any other way...

Without getting dirty obvs

[Kijana Woodard]

Ok. The order line example doesn't work either because that doesn't make much sense as separate docs.

At any rate, references on both docs should work.

[Wayne Douglas]

Yeah that's what I meant when I said it doesn't really fit the bill. I just wanted to get across the idea that this wasn't a tree structure.

At any rate - I'm not sure what putting the references in the parent buys me? I can hold the Ids anywhere - but if they are in the parent what will that get me? How can I use that to construct the view model?

[Kijana Woodard]

If your index is on the parent, you can easily reference the children, and vice versa. Useful in the map and result transforms.