DevForce Community Forum : Generic Distinct Projection

Generic Distinct Projection : Hi Calvin, Sorry if it wasn't...

Tue, 25 Jan 2011 16:29:09 -700

Author: sbelini
Subject: 2465
Posted: 25-Jan-2011 at 4:29pm

Hi Calvin,

Sorry if it wasn't clear in my previous post, but this feature is not available yet.

Like I previously mentioned, the above mentioned feature (returning projections in a query built dynamically) will be available with DevForce2010 v6.0.9.0.

The snippets I provided are only to demonstrate what DevForce can accomplish as of now.

Best regards,

Silvio.

Generic Distinct Projection : Thanks for the reply Silvio.You're...

Tue, 25 Jan 2011 16:03:17 -700

Author: CalvinC
Subject: 2465
Posted: 25-Jan-2011 at 4:03pm

Thanks for the reply Silvio.

You're demo constructs the Where clause dynamically. That's certainly useful; but it's not what I'm asking about.

I want to know if it's possible to construct a Select clause dynamically (an anonymous projection) and then subsequently append a Distinct clause.

I.e, is there a way to construct this line

.Select(e => new {Name = e.FirstName, e.City})

dynamically (where FirstName and City are supplied as parameters)?

Generic Distinct Projection : Hi Calvin, This is a feature...

Tue, 25 Jan 2011 15:35:51 -700

Author: sbelini
Subject: 2465
Posted: 25-Jan-2011 at 3:35pm

Hi Calvin,

This is a feature that will be available with DevForce2010 v6.0.9.0. (returning projections in a query built dynamically)

Right now you can build the query dynamically, but it will return a collection of the Entity type being queried:

var expr1 = PredicateBuilder.Make(typeof(Employee), "LastName"

, FilterOperator.StartsWith

, "D");

var expr2 = PredicateBuilder.Make(typeof(Employee), "Country"

, FilterOperator.IsEqualTo

, "USA");

var expr12 = expr1.And(expr2);

var exprFunc = (Expression<Func<Employee, bool>>)expr12.ToLambdaExpression();

var query = mgr.Employees.Where(exprFunc);

var results = query.Execute(); // results is a collection of Employee

You can always query your large table and return a projection with only the desired fields:

var query = mgr.Employees

.Where(e => e.LastName.StartsWith("D") && Country.Equals("USA"))

.Select(e => new {Name = e.FirstName, e.City});

var results = query.Execute(); // results is a collection of projection { Name, City }

Note that upon execution a query will always return IEnumerable where T is an Entity type or a projection.

Silvio.

Generic Distinct Projection : I have a large flat legacy table that...

Mon, 24 Jan 2011 15:51:39 -700

Author: CalvinC
Subject: 2465
Posted: 24-Jan-2011 at 3:51pm

I have a large flat legacy tablethat has many columns. I would like to writea generic method that can fetch the distinct values in any two columns:

IEnumerable FetchUniqueValues(

Expression> toTypeT1,

Expression> toTypeT2)

{

}

Is there a clever way to accomplishthis with DevForce?

Thanks!