Praveen Praveen - 1 year ago 126
SQL Question

Calling a SQL User-defined function in a LINQ query

I am having a hard time getting this to work. I am trying to do a radius search using the following Filter helper on an IQueryable. There are a set of other filters that get applied before RadiusSearch applies. The order shouldn't really matter since the goal is to get the query to be deferred until a ToList() operation.

public static IQueryable<ApiSearchCommunity> RadiusSearch(this IQueryable<ApiSearchCommunity> communities)
var centerLatitude = 30.421278;
var centerLongitude = -97.426261;
var radius = 25;

return communities.Select(c => new ApiSearchCommunity()
CommunityId = c.CommunityId,
City = c.City,
//Distance = c.GetArcDistance(centerLatitude, centerLongitude, c.Latitude, c.Longitude, radius)

Can I somehow write a helper like GetArcDistance above which in turn calls a UDF on SQL? The query I am trying to generate is the following

) AS distance
FROM communities c) AS comms
WHERE comms.distance <= 25
ORDER BY comms.distance

Answer Source

Ok, I think I understand the question - the gist of it is you want to be able to call a SQL UDF as part of your Linq to Entities query.

This is if you're using database or model first:

This article explains how to do it:

To sum it up, you first need to edit your edmx file in an xml editor, in the edmx:StorageModels >> Schema section you need to specify a mapping to your sql udf, eg

<Function Name="SampleFunction" ReturnType="int" Schema="dbo">
    <Parameter Name="Param" Mode="In" Type="int" />

Then you need to create a static function somewhere with the EdmFunction attribute on it, something like this:

public static class ModelDefinedFunctions
    [EdmFunction("TestDBModel.Store", "SampleFunction")]
    public static int SampleFunction(int param)
      throw new NotSupportedException("Direct calls are not supported.");

This method will get mapped to the UDF at query time by entity framework. The first attribute argument is the store namespace - you can find this in your edmx xml file on the Schema element (look for Namespace). The second argument is the name of the udf.

You can then call it something like this:

var result = from s in context.UDFTests
            select new
                TestVal = ModelDefinedFunctions.SampleFunction(22)

Hope this helps.

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