To call SelectMany dynamically in the way of System.Linq.Dynamic - dynamicquery

Question

In System.Linq.Dynamic, there are a few methods to form Select, Where and other Linq statements dynamically. But there is no for SelectMany.
The method for Select is as the following:
public static IQueryable Select(this IQueryable source, string selector, params object[] values)
{
if (source == null) throw new ArgumentNullException("source");
if (selector == null) throw new ArgumentNullException("selector");
LambdaExpression lambda = DynamicExpression.ParseLambda(source.ElementType, null, selector, values);
IQueryable result = source.Provider.CreateQuery(
Expression.Call(
typeof(Queryable), "Select",
new Type[] { source.ElementType, lambda.Body.Type },
source.Expression, Expression.Quote(lambda)));
return result;
}
I tried to modify the above code, after hours working, I couldn't find a way out.
Any suggestions are welcome.
Ying

Answer 1

Already implemented this one for our project, let me know if it works for you!
public static IQueryable SelectMany(this IQueryable source, string selector, params object[] values)
{
if (source == null)
throw new ArgumentNullException("source");
if (selector == null)
throw new ArgumentNullException("selector");
// Parse the lambda
LambdaExpression lambda =
DynamicExpression.ParseLambda(source.ElementType, null, selector, values);
// Fix lambda by recreating to be of correct Func<> type in case
// the expression parsed to something other than IEnumerable<T>.
// For instance, a expression evaluating to List<T> would result
// in a lambda of type Func<T, List<T>> when we need one of type
// an Func<T, IEnumerable<T> in order to call SelectMany().
Type inputType = source.Expression.Type.GetGenericArguments()[0];
Type resultType = lambda.Body.Type.GetGenericArguments()[0];
Type enumerableType = typeof(IEnumerable<>).MakeGenericType(resultType);
Type delegateType = typeof(Func<,>).MakeGenericType(inputType, enumerableType);
lambda = Expression.Lambda(delegateType, lambda.Body, lambda.Parameters);
// Create the new query
return source.Provider.CreateQuery(
Expression.Call(
typeof(Queryable), "SelectMany",
new Type[] { source.ElementType, resultType },
source.Expression, Expression.Quote(lambda)));
}

Answer 2

I have added another SelectMany that retuns an AnonymousType.
public static IQueryable SelectMany(this IQueryable source, string selector, string resultsSelector, params object[] values)
{
if (source == null)
throw new ArgumentNullException("source");
if (selector == null)
throw new ArgumentNullException("selector");
// Parse the lambda
LambdaExpression lambda =
DynamicExpression.ParseLambda(source.ElementType, null, selector, values);
// Fix lambda by recreating to be of correct Func<> type in case
// the expression parsed to something other than IEnumerable<T>.
// For instance, a expression evaluating to List<T> would result
// in a lambda of type Func<T, List<T>> when we need one of type
// an Func<T, IEnumerable<T> in order to call SelectMany().
Type inputType = source.Expression.Type.GetGenericArguments()[0];
Type resultType = lambda.Body.Type.GetGenericArguments()[0];
Type enumerableType = typeof(IEnumerable<>).MakeGenericType(resultType);
Type delegateType = typeof(Func<,>).MakeGenericType(inputType, enumerableType);
lambda = Expression.Lambda(delegateType, lambda.Body, lambda.Parameters);
ParameterExpression[] parameters = new ParameterExpression[] {
Expression.Parameter(source.ElementType, "outer"), Expression.Parameter(resultType, "inner") };
LambdaExpression resultsSelectorLambda = DynamicExpression.ParseLambda(parameters, null, resultsSelector, values);
// Create the new query
return source.Provider.CreateQuery(
Expression.Call(
typeof(Queryable), "SelectMany",
new Type[] { source.ElementType /*TSource*/, /*,TCollection*/resultType /*TResult*/, resultsSelectorLambda.Body.Type},
source.Expression, Expression.Quote(lambda), Expression.Quote(resultsSelectorLambda)));
}
I still need to figure out how to do the following using Dynamic, the goal is to return a new result object.
var customerandorderflat = db.Customers
.SelectMany(c => c.Orders.SelectMany(o => o.Order_Details,
(ord, orddetail) => new
{
OrderID = ord.OrderID,
UnitPrice = orddetail.UnitPrice
}).DefaultIfEmpty(),
(cus, ord) => new
{
CustomerId = cus.CustomerID,
CompanyName = cus.CompanyName,
OrderId = ord.OrderID == null ? -1 : ord.OrderID,
UnitPrice = ord.UnitPrice
});

Answer 3

I am using the NWDB when I try:
var customerandorderquery = db.Customers .SelectMany(c => c.Orders.DefaultIfEmpty()).Select("new(CustomerId, CompanyName, OrderId)");
I get an error because CompanyName is in Customers not Orders. So it is not seeing the combination of the two objects.
When I do:
.SelectMany(c => c.Orders.DefaultIfEmpty(), (cus, ord) => new { CustomerId = cus.CustomerID, OrderId = ord.OrderID == null ? -1 : ord.OrderID });
It returns the desired result.