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Kendo MVC Grid DataSourceRequest with AutoMapper - Advance

The actual process to make DataSourceRequest compatible with AutoMapper was explained in my previous post Kendo MVC Grid DataSourceRequest with AutoMapper, where we had created custom model binder attribute and in that property names were changed as data models.

In this post we will be looking into using AutoMapper's Queryable extension to retrieve the results based on selected columns. When Mapper.Map<RoleViewModel>(data) is called it retrieves all column values from table. The Queryable extension provides a way to retrieve only selected columns from table. In this particular case based on properties of RoleViewModel.

The previous approach that we implemented is perfect as far as this article (3 Tips for Using Telerik Data Access and AutoMapper) is concern about performance where it states:
While this functionality allows you avoid writing explicit projection in to your LINQ query it has the same fatal flaw as doing so - it prevents the query result from being cached.
Since this can have a strong negative impact on the performance even though only minimal amount of data is retrieved, we advise you not to use AutoMapper projection in LINQ queries. Instead we recommend you map the instances of your persistent types after they have been completely retrieved in memory using the Map method of AutoMapper.
I am not against or in favour of any approach it all depends on requirement. If we have tables with large number of columns then it won't be good approach. So, if you plan to go with AutoMapper extension for projection then only follow ahead.

ToDataSourceResult is an extension method from Kendo, which internally takes care of projection with different sorts, filters, groups and aggregates. We need all these features except the projection that need to handled by us using AutoMapper. The ToDataSourceResult uses "Kendo.Mvc.Extensions.CreateDataSourceResult" function to form mentioned features. 

This is a only part of code that we need to implement for having AutoMapper Linq Projection:

     /// <summary>  
     /// Creates the data source result.  
     /// </summary>  
     /// <typeparam name="TModel">The type of the model.</typeparam>  
     /// <typeparam name="TResult">The type of the result.</typeparam>  
     /// <param name="queryable">The queryable.</param>  
     /// <param name="request">The request.</param>  
     /// <returns>Kendo Data source result</returns>  
     /// <remarks>MODIFICATION OF "Kendo.Mvc.Extensions.CreateDataSourceResult" TO IMPLEMENT AUTOMAPPER PROJECTION.</remarks>  
     public static DataSourceResult CreateDataSourceResult<TModel, TResult>(this IQueryable<TModel> queryable, DataSourceRequest request)  
       Func<AggregateDescriptor, IEnumerable<AggregateFunction>> aggregates = null;  
       var dataSourceResult = new DataSourceResult();  
       IQueryable queryables = queryable;  
       var filterDescriptors = new List<IFilterDescriptor>();  
       if (request.Filters != null)  
       if (filterDescriptors.Any<IFilterDescriptor>())  
         queryables = queryables.Where(filterDescriptors);  
       var sortDescriptors = new List<SortDescriptor>();  
       if (request.Sorts != null)  
       var sortDescriptors1 = new List<SortDescriptor>();  
       var groupDescriptors = new List<GroupDescriptor>();  
       if (request.Groups != null)  
       var aggregateDescriptors1 = new List<AggregateDescriptor>();  
       if (request.Aggregates != null)  
       if (aggregateDescriptors1.Any<AggregateDescriptor>())  
         IQueryable queryables1 = queryables.AsQueryable();  
         IQueryable queryables2 = queryables1;  
         if (filterDescriptors.Any<IFilterDescriptor>())  
           queryables2 = queryables1.Where(filterDescriptors);  
         dataSourceResult.AggregateResults = queryables2.Aggregate(aggregateDescriptors1.SelectMany<AggregateDescriptor, AggregateFunction>((AggregateDescriptor a) => a.Aggregates));  
         if (groupDescriptors.Any<GroupDescriptor>() && aggregateDescriptors1.Any<AggregateDescriptor>())  
           groupDescriptors.Each<GroupDescriptor>((GroupDescriptor g) =>  
             AggregateFunctionCollection aggregateFunctions = g.AggregateFunctions;  
             List<AggregateDescriptor> aggregateDescriptors = aggregateDescriptors1;  
             if (aggregates == null)  
               aggregates = (AggregateDescriptor a) => a.Aggregates;  
             aggregateFunctions.AddRange<AggregateFunction>(aggregateDescriptors.SelectMany<AggregateDescriptor, AggregateFunction>(aggregates));  
       dataSourceResult.Total = queryables.Count();  
       if (groupDescriptors.Any<GroupDescriptor>())  
         groupDescriptors.Reverse<GroupDescriptor>().Each<GroupDescriptor>((GroupDescriptor groupDescriptor) =>  
           SortDescriptor sortDescriptor3 = new SortDescriptor()  
             Member = groupDescriptor.Member,  
             SortDirection = groupDescriptor.SortDirection  
           sortDescriptors.Insert(0, sortDescriptor3);  
       if (sortDescriptors.Any<SortDescriptor>())  
         queryables = queryables.Sort(sortDescriptors);  
       IQueryable queryables3 = queryables;  
       queryables = queryables.Page(request.Page - 1, request.PageSize);  
       if (groupDescriptors.Any<GroupDescriptor>())  
         queryables = queryables.GroupBy(queryables3, groupDescriptors);  
       dataSourceResult.Data = (queryables as IQueryable<TModel>).Execute<TModel, TResult>();  
       sortDescriptors1.Each<SortDescriptor>((SortDescriptor sortDescriptor) => sortDescriptors.Remove(sortDescriptor));  
       return dataSourceResult;  
     /// <summary>  
     /// Executes the specified source.  
     /// </summary>  
     /// <typeparam name="TModel">The type of the model.</typeparam>  
     /// <typeparam name="TResult">The type of the result.</typeparam>  
     /// <param name="source">The source.</param>  
     /// <returns></returns>  
     /// <exception cref="System.ArgumentNullException">source</exception>  
     /// <remarks>MODIFICATION OF "Kendo.Mvc.Extensions.Execute" TO IMPLEMENT AUTOMAPPER PROJECTION.</remarks>  
     private static IEnumerable Execute<TModel, TResult>(this IQueryable<TModel> source)  
       if (source == null)  
         throw new ArgumentNullException("source");  
       Type elementType = source.ElementType;  
       if (elementType != typeof(AggregateFunctionsGroup))  
         return source.Project().To<TResult>();  
       // TODO: Need to test with grouping  
       List<AggregateFunctionsGroup> aggregateFunctionsGroups = new List<AggregateFunctionsGroup>();  
       foreach (AggregateFunctionsGroup aggregateFunctionsGroup in source as IQueryable)  
         var aggregateQuerable = aggregateFunctionsGroup.Items.AsQueryable() as IQueryable<TModel>;  
         if (aggregateQuerable != null)  
           aggregateFunctionsGroup.Items = aggregateQuerable.Execute<TModel, TResult>();  
       return aggregateFunctionsGroups;  

If we see above code we only have two functions but both of them are having same code as whatever Kendo is providing with very few changes. The CreateDataSourceResult function is responsible for different sorts, filters, groups and aggregates but the actual call is happening under Execute function. To implement AutoMapper Linq Projection we only needed to modify Execute function but since it is only through CreateDataSourceResult, we need to modify both.

This is return source.Project().To<TResult>(); only change done under Execute function for mapping.

NOTE: I have not tested it with grouping. Possibly that might be the reason, Kendo did not provided some kind injection for mapping.

After that being setup we only need to call in this way.

 queryable.CreateDataSourceResult<RoleDomainModel, RoleViewModel>(request)  
 // Another example
 UnitOfWork.RoleRepository.All().CreateDataSourceResult<RoleDomainModel, RoleViewModel>(request);  

If you want, we can have similar implementation like Kendo by creating our own version of extension method ToDataSourceResult which can consume our created functions.

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