private static IQueryable ApplyFilter(IQueryable queryable, Query query)
{
var parameter = Expression.Parameter(queryable.ElementType);
var expression = query.Filter.CreateExpression(parameter);
if (expression == null)
return queryable;
var lambda = Expression.Lambda(expression, parameter);
var ordercall = Expression.Call(typeof(Queryable), "Where", new[] { queryable.ElementType }, queryable.Expression, lambda);
return queryable.Provider.CreateQuery(ordercall);
}
public QueryResult Execute(IQueryable queryable, Query query)
{
queryable = ApplyFilter(queryable, query);
var totalAvailable = DetermineTotalAvailable(queryable);
queryable = ApplySorting(queryable, query);
queryable = ApplyPaging(queryable, query);
queryable = ApplySelection(queryable, query);
var assets = InternalExecute(queryable, query);
return new QueryResult(query, assets, totalAvailable);
}
private static IQueryable ApplySelection(IQueryable queryable, Query query)
{
var typeName = $"t{Guid.NewGuid().ToString("N")}";
var typeBuilder = ModuleBuilder.DefineType(typeName);
var parameter = Expression.Parameter(queryable.ElementType);
var selectionFieldMapping = GetSelectionMapping(query.Selection);
IDictionary<string, Expression> mapping = new Dictionary<string, Expression>();
foreach (var kvp in selectionFieldMapping)
{
var name = kvp.Key;
var attributeDefinition = kvp.Value;
var expression = attributeDefinition.CreateExpression(parameter);
mapping.Add(name, expression);
var fieldType = expression.Type;
typeBuilder.DefineField(name, fieldType, FieldAttributes.Public);
}
var generatedType = typeBuilder.CreateType();
List<MemberAssignment> bindings = new List<MemberAssignment>();
foreach (var kvp in mapping)
{
var propertyName = kvp.Key;
var rightExpression = kvp.Value;
var targetField = generatedType.GetField(propertyName);
var binding = Expression.Bind(targetField, rightExpression);
bindings.Add(binding);
}
var newContext = Expression.New(generatedType);
var memberInit = Expression.MemberInit(newContext, bindings);
var select = Expression.Lambda(memberInit, parameter);
var call = Expression.Call(typeof(Queryable), "Select", new[] { queryable.ElementType, @select.ReturnType }, queryable.Expression, @select);
return queryable.Provider.CreateQuery(call);
}
private static IQueryable ApplyPaging(IQueryable queryable, Query query)
{
if (query.Skip.HasValue)
{
var skip = Expression.Constant(query.Skip.Value);
var call = Expression.Call(typeof(Queryable), "Skip", new[] { queryable.ElementType }, queryable.Expression, skip);
queryable = queryable.Provider.CreateQuery(call);
}
if (query.Take.HasValue)
{
var take = Expression.Constant(query.Take.Value);
var call = Expression.Call(typeof(Queryable), "Take", new[] { queryable.ElementType }, queryable.Expression, take);
queryable = queryable.Provider.CreateQuery(call);
}
return queryable;
}
public QueryResult(Query query, IEnumerable<Asset> assets, long totalAvailable)
{
Query = query;
Assets = assets;
TotalAvailable = totalAvailable;
}
private static IEnumerable<Asset> InternalExecute(IQueryable queryable, Query query)
{
List<Asset> assets = new List<Asset>();
var selectionFieldMapping = GetSelectionMapping(query.Selection);
var fieldMap = queryable.ElementType.GetFields().ToDictionary(x => x.Name);
foreach (var obj in queryable)
{
Asset asset = new Asset(query.AssetType);
foreach (var kvp in selectionFieldMapping)
{
var name = kvp.Key;
var attributeDefinition = kvp.Value;
var field = fieldMap[name];
var value = field.GetValue(obj);
asset.LoadAttribute(attributeDefinition, value);
}
assets.Add(asset);
}
return assets;
}
private static IQueryable ApplySorting(IQueryable queryable, Query query)
{
bool first = true;
foreach (var term in query.OrderTerms)
{
string methodName = null;
if (first)
methodName = term.Direction == OrderTermDirection.Ascending ? "OrderBy" : "OrderByDescending";
else
methodName = term.Direction == OrderTermDirection.Ascending ? "ThenBy" : "ThenByDescending";
first = false;
var parameter = Expression.Parameter(queryable.ElementType);
var expression = term.AttributeDefinition.CreateExpression(parameter);
var lambda = Expression.Lambda(expression, parameter);
var ordercall = Expression.Call(typeof(Queryable), methodName, new [] { queryable.ElementType, lambda.ReturnType }, queryable.Expression, lambda);
queryable = queryable.Provider.CreateQuery(ordercall);
}
return queryable;
}
