Entity Framework 6 Code First Custom Functions

Entity Framework 6 Code First Custom Functions

You should be able to use a scalar SQL function in your Where criterias with CodeFirstStoreFunctions

Assuming you want to map SQL function [dbo].[LatLongDistanceCalc], and according to the test suite:

public class MyDataContext: DbContext
{
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
       //...

       modelBuilder.Conventions.Add(new FunctionsConvention("dbo", this.GetType()));
    }

    // "CodeFirstDatabaseSchema" is a convention mandatory schema name
    // "LatLongDistanceCalc" is the name of your function

    [DbFunction("CodeFirstDatabaseSchema", "LatLongDistanceCalc")]
    public static int LatLongDistanceCalc(int fromLat, int fromLong,
                                                       int toLat, int toLong)
    {
       // no need to provide an implementation
       throw new NotSupportedException();
    }
}

usage would then be:

context.Locations
       .Where(e => MyDataContext.LatLongDistanceCalc(e.Lat, e.Long, lat, long) >= 10)

Using EF6 Store Functions for Entity Framework code-first, can I return a custom type?

The type to be returned must have columns named the same as the function. For example, if the function returns columns:

Name nvarchar
Sum  int

then SomeClassSummary should be:

public class SomeClassSummary {
    public string Name { get; set; }
    public int Sum { get; set; }
}

Then in the context, add the class as a complex type:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.ComplexType<SomeClassSummary>();
    modelBuilder.Conventions.Add(new FunctionsConvention<MyContext>("dbo"));
}

Entity Framework Code First Function

This may provide an answer to what you need.

Code first Entity Framework 6.1 Custom Aggregate Function

As @srutzky alluded to in the comments, EF doesnt seem to like binding to aggregate functions with multiple parameters. So you have to change percentile function to a median function or whatever fixed percentile you are interested (you will need to update your SqlClr function so the parameters match as well)

public class MySqlFunctions
{
    [DbFunction("dbo", "Median")]
    public static float? Median(IEnumerable<float?> arg)
    {
        throw new NotSupportedException("Direct calls are not supported.");
    }
}

The next step is letting EF know that a the database has a function called median We can do this in our DbContext. Create a new convention to access the the dbModel then we add the function in the dbModel. You must make sure the parameters and the parameter types match both the SQL and the C# function exactly.

public class EmContext : DbContext
{    
    ...

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        //Register a convention so we can load our function
        modelBuilder.Conventions.Add(new AddMedianFunction());

        ...

    }

    public class AddMedianFunction : IConvention, IStoreModelConvention<EntityContainer>
    {
        public void Apply(EntityContainer item, DbModel dbModel)
        {
            //these parameter types need to match both the database method and the C# method for EF to link
            var edmFloatType = PrimitiveType.GetEdmPrimitiveType(PrimitiveTypeKind.Single);

            //CollectionType constructor is internal making it impossible to get a collection type. 
            //We resort to reflection instantiation.
            var edmFloatListType = CreateInstance<CollectionType>(edmFloatType);

            var medianfunction = EdmFunction.Create("Median", "dbo", DataSpace.SSpace, new EdmFunctionPayload
            {
                ParameterTypeSemantics = ParameterTypeSemantics.AllowImplicitConversion,
                IsComposable = true,
                IsAggregate = true,
                Schema = "dbo",
                ReturnParameters = new[]
                {
                    FunctionParameter.Create("ReturnType", edmFloatType, ParameterMode.ReturnValue)
                },
                Parameters = new[]
                {
                    FunctionParameter.Create("input", edmFloatListType, ParameterMode.In),
                }
            }, null);

            dbModel.StoreModel.AddItem(medianfunction);
            dbModel.Compile();       
        }

        public static T CreateInstance<T>(params object[] args)
        {
            var type = typeof(T);
            var instance = type.Assembly.CreateInstance(
                type.FullName, false,
                BindingFlags.Instance | BindingFlags.NonPublic,
                null, args, null, null);
            return (T)instance;
        }
    }
}

With all that in place you should just be able to call your function as expected

paymentsTable
    .GroupBy(x=>x.CustomerId)
    .Select(new{
            Median = MySqlFunctions.Median(x.Select(g=>g.Amount))
    });

Note: I am already assume you have loaded your SqlClr function which I have not covered here

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