Service

using System.Linq;

namespace Terrasoft.Configuration
{

    using System.ServiceModel;
    using System.ServiceModel.Web;
    using System.ServiceModel.Activation;
    using System.Web;
    using System;
    using System.Collections.Generic;
    using System.Collections.ObjectModel;
    using System.Data;
    using Terrasoft.Common;
    using Terrasoft.Core.DB;
    using Terrasoft.Core.Entities;
    using Terrasoft.Core;

    [ServiceContract]
    [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Required)]
    public class StorageService
    {
        private UserConnection _userConnection;
        private UserConnection UserConnection {
            get {
                return _userConnection ?? (_userConnection = HttpContext.Current
                .Session["UserConnection"] as UserConnection);
            }
        }

        #region Constructors: Public

        public StorageService() {}

        public StorageService(UserConnection userConnection) {
            _userConnection = userConnection;
        }

        #endregion

        private decimal GetEntityArea(Guid entityId, string tableName)
        {
            // FIRST VARIANT
            //EntitySchema schema = UserConnection.EntitySchemaManager.FindInstanceByName(tableName);
            //Entity entity = schema.CreateEntity(UserConnection);
            //entity.FetchFromDB("Id", entityId, new[] {"UsrArea"});

            // SECOND VARIANT
            var esqResult = new EntitySchemaQuery(UserConnection.EntitySchemaManager, tableName);
            esqResult.AddColumn("UsrArea");

            var storageCapacityEntity = esqResult.GetEntity(UserConnection, entityId);

            return storageCapacityEntity.GetTypedColumnValue<decimal>("UsrArea");
        }

        private decimal GetUsedStorageArea(Guid storageId) {
            // FIRST VARIANT
            //var esqResult = new EntitySchemaQuery(UserConnection.EntitySchemaManager, "UsrStorage");
            //var totalUsrAreaColumn = esqResult.AddColumn(esqResult.CreateAggregationFunction(AggregationTypeStrict.Sum, "[UsrStuff:UsrStorage:Id].UsrArea"));
            //esqResult.Filters.Add(esqResult.CreateFilterWithParameters(FilterComparisonType.Equal, "Id", storageId));
            //var storageUsedCapacityEntity = esqResult.GetEntityCollection(UserConnection).FirstOrDefault();

            //return storageUsedCapacityEntity.GetTypedColumnValue<decimal>(totalUsrAreaColumn.Name);

            // SECOND VARIANT
            var esqResult = new EntitySchemaQuery(UserConnection.EntitySchemaManager, "UsrStuff");
            esqResult.AddColumn("UsrArea");
            esqResult.Filters.Add(esqResult.CreateFilterWithParameters(FilterComparisonType.Equal, "UsrStorage", storageId));
            var entityCollection = esqResult.GetEntityCollection(UserConnection);
            var resultUsrArea = entityCollection.Sum(x => x.GetTypedColumnValue<decimal>("UsrArea"));
            return resultUsrArea;
        }

        [OperationContract]
        [WebInvoke(Method = "GET", UriTemplate = "CheckStorageCapacity?storageId={storageId}&stuffId={stuffId}", ResponseFormat = WebMessageFormat.Json)]
        public bool CheckStorageCapacity(Guid storageId, Guid stuffId)
        {
            var stuffArea = GetEntityArea(stuffId, "UsrStuff");
            var storageArea = GetEntityArea(storageId, "UsrStorage");
            var storageUsedArea = GetUsedStorageArea(storageId);
            var freeStorageArea = storageArea - storageUsedArea;

            return stuffArea <= freeStorageArea;
        }
    }
}