how to modify or insert where into expression tree - linq

Question

by default I have this:
Expression<Func<ItemGroup, ItemGroupView>> Exp =
m => new ItemGroupView{
ID = m.id,
Name = m.name,
TotalCount = m.groupDetail.Sum(n => n.item.itemDetail.Count())
};
but in the runtime, I might want to add multiple filter. So for example, if I specify the status to 1 and category to mineral then it becomes
Expression<Func<ItemGroup, ItemGroupView>> Exp =
m => new ItemGroupView{
ID = m.id,
Name = m.name,
TotalCount = m.groupDetail.Sum(
n => n.item.itemDetail
.Where(o => o.status == 1 && o.category == "mineral")
.Count())
};
// ItemGroup.groupDetail is collection of ItemGroupDetail (n)
// ItemGroupDetail.item is Item
// Item.itemDetail is collection of ItemDetail (o)
// ItemDetail.item is Item
how do I modify the expression tree to insert multiple Where dynamically?
So far I do the default like this
private int _status;
private string _category;
internal Expression<Func<ItemDetail, bool>> whereStatus()
{
return o => o.status == _status;
}
internal Expression<Func<ItemDetail, bool>> whereCategory()
{
return o => o.category == _category ;
}
internal Expression<Func<ItemGroup, ItemGroupView>> GetEx()
{
return m => new ItemGroupView{
ID = m.id,
Name = m.name,
TotalCount = m.groupDetail.Sum(n => n.item.itemDetail.Count())
};
}
internal IQueryable<ItemGroupView> GetSelectQuery(IQueryabe<ItemGroup> ie)
{
ParameterExpression m = Expression.Parameter(typeof(ItemGroup), "m");
ParameterExpression n = Expression.Parameter(typeof(ItemGroupDetail), "n");
MemberInitExpression ex = (MemberInitExpression)GetEx().Body;
// ParameterReplacer is inherited from ExpressionVisitor
ex = (MemberInitExpression)new ParameterReplacer(
new ParameterExpression[] { m, n }).Visit(ex);
// ? ? ? ?
// how to modify the Expression if _status or _category is supplied?
Expression<Func<ItemGroup, ItemGroupView>> el =
Expression.Lambda<Func<ItemGroup, ItemGroupView>>
(ex, new ParameterExpression { m });
return ie.Select(el);
}
EDIT:
ItemGroup.itemDetail changed to ItemGroup.groupDetail, to avoid confusion between groups and items..

Answer 1

If you can create an expression that represents the Where() operation, you can then paste it into your main expression using LINQKit:
Expression<Func<IQueryable<ItemDetail>, IQueryable<ItemDetail>>> whereExpression=
id => id.Where(o => o.status == 1 && o.category == "mineral");
Expression<Func<ItemGroup, ItemGroupView>> Exp =
m => new ItemGroupView
{
ID = m.id,
Name = m.name,
TotalCount =
whereExpression.Invoke(m.itemDetail)
.Sum(n => n.item.itemDetail.Count())
};
Exp = Exp.Expand();
(Don't forget that last line, it's important.)