using stored procedure in entity framework

You need to create a model class that contains all stored procedure properties like below.
Also because Entity Framework model class needs primary key, you can create a fake key by using Guid.

public class GetFunctionByID
{
    [Key]
    public Guid? GetFunctionByID { get; set; }

    // All the other properties.
}

then register the GetFunctionByID model class in your DbContext.

public class FunctionsContext : BaseContext<FunctionsContext>
{
    public DbSet<App_Functions> Functions { get; set; }
    public DbSet<GetFunctionByID> GetFunctionByIds {get;set;}
}

When you call your stored procedure, just see below:

var functionId = yourIdParameter;
var result =  db.Database.SqlQuery<GetFunctionByID>("GetFunctionByID @FunctionId", new SqlParameter("@FunctionId", functionId)).ToList());