.Query<T> for a T with nested objects

c# dapper orm

Question

Possible Duplicate:
How do I select an aggregate object efficiently using Dapper?

is it possible to get dapper to instantiate nested objects, and if so, are there any examples of this in action?

For most situations, .net primitives are sufficient for me, but not always. A hack might be to include the foreign key as primitives in the parent type, and then instantiate based on these afterwards. I'm hoping this isn't necessary as it would create unwanted noise in the POCO model.

Accepted Answer

I think the helper I propose here: Multi-Mapper to create object hierarchy may be of help.

var mapped = cnn.QueryMultiple(sql)
   .Map<A,B,A>
    (
       A => A.ID, 
       B => B.AID,
       a, bees => { A.Items = bees};  
    );

Assuming you extend your GridReader and with a mapper:

public static IEnumerable<TFirst> Map<TFirst, TSecond, TKey>
    (
    this GridReader reader,
    Func<TFirst, TKey> firstKey, 
    Func<TSecond, TKey> secondKey, 
    Action<TFirst, IEnumerable<TSecond>> addChildren
    )
{
    var first = reader.Read<TFirst>().ToList();
    var childMap = reader
        .Read<TSecond>()
        .GroupBy(s => secondKey(s))
        .ToDictionary(g => g.Key, g => g.AsEnumerable());

    foreach (var item in first)
    {
        IEnumerable<TSecond> children;
        if(childMap.TryGetValue(firstKey(item), out children))
        {
            addChildren(item,children);
        }
    }

    return first;
}

You could extend this pattern to work with a 3 level hierarchy.




Licensed under: CC-BY-SA with attribution
Not affiliated with Stack Overflow
Is this KB legal? Yes, learn why
Licensed under: CC-BY-SA with attribution
Not affiliated with Stack Overflow
Is this KB legal? Yes, learn why