How to dynamically order by certain entity properties in Entity Framework 7 (Core)

Question

I have a project where the front-end JavaScript specifies a list of columns to order by.

Then in the back-end I have multi-layer application. Typical scenario

1. Service layer (the service models' (DTO) properties match whatever the client-side wants to order by)
2. Domain layer (it exposes repository interfaces to access persisted objects)
3. ORM layer (it implements the repository and it uses Entity Framework 7 (a.k.a Entity Framework Core) to access a SQL Server database)

Please note that System.Linq.Dynamic IS NOT supported for DNX Core v5.0 or .NET Platform v5.4 so I cannot use that library.

I have the following implementation in my Things repository:

    public async Task<IEnumerable<Thing>> GetThingsAsync(IEnumerable<SortModel> sortModels)
    {
        var query = GetThingsQueryable(sortModels);
        var things = await query.ToListAsync();
        return things;
    }

    private IQueryable<Thing> GetThingsQueryable(IEnumerable<SortModel> sortModels)
    {

        var thingsQuery = _context.Things
                .Include(t => t.Other)
                .Where(t => t.Deleted == false);

        // this is the problematic area as it does not return a valid queryable
        string orderBySqlStatement = GetOrderBySqlStatement(sortModels);
        thingsQuery = thingsQuery.FromSql(orderBySqlStatement);
        return thingsQuery ;
    }

    /// this returns something like " order by thingy1 asc, thingy2 desc"
    private string GetOrderBySqlStatement(IEnumerable<SortModel> sortModels)
    {
        IEnumerable<string> orderByParams = sortModels.Select(pair => { return pair.PairAsSqlExpression; });
        string orderByParamsConcat = string.Join(", ", orderByParams);
        string sqlStatement = orderByParamsConcat.Length > 1 ? $" order by {orderByParamsConcat}" : string.Empty;
        return sqlStatement;
    }

and this is the object that contains a column name and a order by direction (asc or desc)

public class SortModel
{
    public string ColId { get; set; }
    public string Sort { get; set; }

    public string PairAsSqlExpression
    {
        get
        {
            return $"{ColId} {Sort}";
        }
    }
}

This approach tries to mix a SQL statement with whatever Entity creates for the previous queryable. But I get a:

Microsoft.Data.Entity.Query.Internal.SqlServerQueryCompilationContextFactory:Verbose: Compiling query model: 'from Thing t in {value(Microsoft.Data.Entity.Query.Internal.EntityQueryable`1[MyTestProj.Data.Models.Thing]) => AnnotateQuery(Include([t].DeparturePort)) => AnnotateQuery(Include([t].ArrivalPort)) => AnnotateQuery(Include([t].Consignments))} where (([t].CreatorBusinessId == __businessId_0) AndAlso (Convert([t].Direction) == __p_1)) select [t] => AnnotateQuery(QueryAnnotation(FromSql(value(Microsoft.Data.Entity.Query.Internal.EntityQueryable`1[MyTestProj.Data.Models.Thing]), " order by arrivalDate asc, arrivalPortCode asc", []))) => Count()'
Microsoft.Data.Entity.Query.Internal.SqlServerQueryCompilationContextFactory:Verbose: Optimized query model: 'from Thing t in value(Microsoft.Data.Entity.Query.Internal.EntityQueryable`1[MyTestProj.Data.Models.Thing]) where (([t].CreatorBusinessId == __businessId_0) AndAlso (Convert([t].Direction) == __p_1)) select [t] => Count()'
Microsoft.Data.Entity.Query.Internal.QueryCompiler:Error: An exception occurred in the database while iterating the results of a query.
System.InvalidOperationException: The Include operation is not supported when calling a stored procedure.
   at Microsoft.Data.Entity.Query.ExpressionVisitors.RelationalEntityQueryableExpressionVisitor.VisitEntityQueryable(Type elementType)
   at Microsoft.Data.Entity.Query.ExpressionVisitors.EntityQueryableExpressionVisitor.VisitConstant(ConstantExpression constantExpression)
   at System.Linq.Expressions.ConstantExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.Data.Entity.Query.ExpressionVisitors.ExpressionVisitorBase.Visit(Expression expression)
   at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.ReplaceClauseReferences(Expression expression, IQuerySource querySource, Boolean inProjection)
   at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.CompileMainFromClauseExpression(MainFromClause mainFromClause, QueryModel queryModel)
   at Microsoft.Data.Entity.Query.RelationalQueryModelVisitor.CompileMainFromClauseExpression(MainFromClause mainFromClause, QueryModel queryModel)
   at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.VisitMainFromClause(MainFromClause fromClause, QueryModel queryModel)
   at Remotion.Linq.Clauses.MainFromClause.Accept(IQueryModelVisitor visitor, QueryModel queryModel)
   at Remotion.Linq.QueryModelVisitorBase.VisitQueryModel(QueryModel queryModel)
   at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
   at Microsoft.Data.Entity.Query.RelationalQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
   at Microsoft.Data.Entity.Query.Internal.SqlServerQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
   at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.CreateAsyncQueryExecutor[TResult](QueryModel queryModel)
   at Microsoft.Data.Entity.Storage.Database.CompileAsyncQuery[TResult](QueryModel queryModel)
   at Microsoft.Data.Entity.Query.Internal.QueryCompiler.<>c__DisplayClass19_0`1.<CompileAsyncQuery>b__0()
   at Microsoft.Data.Entity.Query.Internal.CompiledQueryCache.GetOrAddAsyncQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.Data.Entity.Query.Internal.QueryCompiler.CompileAsyncQuery[TResult](Expression query)
   at Microsoft.Data.Entity.Query.Internal.QueryCompiler.ExecuteAsync[TResult](Expression query, CancellationToken cancellationToken)
Exception thrown: 'System.InvalidOperationException' in EntityFramework.Core.dll
Exception thrown: 'System.InvalidOperationException' in mscorlib.ni.dll
Exception thrown: 'System.InvalidOperationException' in mscorlib.ni.dll
Microsoft.AspNet.Diagnostics.Entity.DatabaseErrorPageMiddleware:Verbose: System.InvalidOperationException occurred, checking if Entity Framework recorded this exception as resulting from a failed database operation.
Microsoft.AspNet.Diagnostics.Entity.DatabaseErrorPageMiddleware:Verbose: Entity Framework recorded that the current exception was due to a failed database operation. Attempting to show database error page.
Microsoft.Data.Entity.Storage.Internal.SqlServerConnection:Verbose: Opening connection 'Server=(localdb)\mssqllocaldb;Database=SpeediCargo;Trusted_Connection=True;MultipleActiveResultSets=true'.
Microsoft.Data.Entity.Storage.Internal.SqlServerConnection:Verbose: Closing connection 'Server=(localdb)\mssqllocaldb;Database=SpeediCargo;Trusted_Connection=True;MultipleActiveResultSets=true'.
Microsoft.Data.Entity.Storage.Internal.SqlServerConnection:Verbose: Opening connection 'Server=(localdb)\mssqllocaldb;Database=SpeediCargo;Trusted_Connection=True;MultipleActiveResultSets=true'.
Microsoft.Data.Entity.Storage.Internal.SqlServerConnection:Verbose: Closing connection 'Server=(localdb)\mssqllocaldb;Database=SpeediCargo;Trusted_Connection=True;MultipleActiveResultSets=true'.
Microsoft.Data.Entity.Storage.Internal.SqlServerConnection:Verbose: Opening connection 'Server=(localdb)\mssqllocaldb;Database=SpeediCargo;Trusted_Connection=True;MultipleActiveResultSets=true'.
Microsoft.Data.Entity.Storage.Internal.RelationalCommandBuilderFactory:Information: Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
SELECT OBJECT_ID(N'__EFMigrationsHistory');
Microsoft.Data.Entity.Storage.Internal.SqlServerConnection:Verbose: Closing connection 'Server=(localdb)\mssqllocaldb;Database=SpeediCargo;Trusted_Connection=True;MultipleActiveResultSets=true'.
Microsoft.Data.Entity.Storage.Internal.SqlServerConnection:Verbose: Opening connection 'Server=(localdb)\mssqllocaldb;Database=SpeediCargo;Trusted_Connection=True;MultipleActiveResultSets=true'.
Microsoft.Data.Entity.Storage.Internal.RelationalCommandBuilderFactory:Information: Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30']

It seems it's not possible to mix SQL for the order by part with the rest of the linq query? Or the problem is that I am not prefixing the columns with the [t] and Entity is unable to understand what are those columns?

In any case, is there any example or recommendation on how to achieve what I want with Entity 7 and the core .net framework?

Answer 1

FromSql definitely cannot be used to mix SQL. So as usual with dynamic queries, you have to resort to System.Linq.Expressions.

For instance, something like this:

public static class QueryableExtensions
{
    public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, IEnumerable<SortModel> sortModels)
    {
        var expression = source.Expression;
        int count = 0;
        foreach (var item in sortModels)
        {
            var parameter = Expression.Parameter(typeof(T), "x");
            var selector = Expression.PropertyOrField(parameter, item.ColId);
            var method = string.Equals(item.Sort, "desc", StringComparison.OrdinalIgnoreCase) ?
                (count == 0 ? "OrderByDescending" : "ThenByDescending") :
                (count == 0 ? "OrderBy" : "ThenBy");
            expression = Expression.Call(typeof(Queryable), method,
                new Type[] { source.ElementType, selector.Type },
                expression, Expression.Quote(Expression.Lambda(selector, parameter)));
            count++;
        }
        return count > 0 ? source.Provider.CreateQuery<T>(expression) : source;
    }
}

And then:

var thingsQuery = _context.Things
        .Include(t => t.Other)
        .Where(t => t.Deleted == false)
        .OrderBy(sortModels);