Simplest way to flatten document to a view in RavenDB
- by degorolls
Given the following classes:
public class Lookup
{
public string Code { get; set; }
public string Name { get; set; }
}
public class DocA
{
public string Id { get; set; }
public string Name { get; set; }
public Lookup Currency { get; set; }
}
public class ViewA // Simply a flattened version of the doc
{
public string Id { get; set; }
public string Name { get; set; }
public string CurrencyName { get; set; } // View just gets the name of the currency
}
I can create an index that allows client to query the view as follows:
public class A_View : AbstractIndexCreationTask<DocA, ViewA>
{
public A_View()
{
Map = docs => from doc in docs
select new ViewA
{
Id = doc.Id,
Name = doc.Name,
CurrencyName = doc.Currency.Name
};
Reduce = results => from result in results
group on new ViewA
{
Id = result.Id,
Name = result.Name,
CurrencyName = result.CurrencyName
} into g
select new ViewA
{
Id = g.Key.Id,
Name = g.Key.Name,
CurrencyName = g.Key.CurrencyName
};
}
}
This certainly works and produces the desired result of a view with the data transformed to the structure required at the client application. However, it is unworkably verbose, will be a maintenance nightmare and is probably fairly inefficient with all the redundant object construction.
Is there a simpler way of creating an index with the required structure (ViewA) given a collection of documents (DocA)?
FURTHER INFORMATION
The issue appears to be that in order to have the index hold the data in the transformed structure (ViewA), we have to do a Reduce. It appears that a Reduce must have both a GROUP ON and a SELECT in order to work as expected so the following are not valid:
INVALID REDUCE CLAUSE 1:
Reduce = results => from result in results
group on new ViewA
{
Id = result.Id,
Name = result.Name,
CurrencyName = result.CurrencyName
} into g
select g.Key;
This produces: System.InvalidOperationException: Variable initializer select must have a lambda expression with an object create expression
Clearly we need to have the 'select new'.
INVALID REDUCE CLAUSE 2:
Reduce = results => from result in results
select new ViewA
{
Id = result.Id,
Name = result.Name,
CurrencyName = result.CurrencyName
};
This prduces: System.InvalidCastException: Unable to cast object of type 'ICSharpCode.NRefactory.Ast.IdentifierExpression' to type 'ICSharpCode.NRefactory.Ast.InvocationExpression'.
Clearly, we also need to have the 'group on new'.
Thanks for any assistance you can provide.
(Note: removing the type (ViewA) from the constructor calls has no effect on the above)
