LINQ: Fill objects from left join

Question

I\'m new to linq. How do I load my objects using LINQ from a left join database query (PostGIS).

This is my database query:

Answer 1

So - if I understand right - you have a database query that you are happy with, but you want to take the row-column shaped result and project it into a hierarchically shaped result.

---

Suppose the results are in a List

public class Row
{
  public int id {get;set;}
  public string type {get;set;}
  public int attid {get;set;}
  public string label {get;set;}
  public int? attvalueid {get;set;}
  public string value {get;set;}
}

Then you would group twice, and turn each top-level group into a Type, each child-level group into an Attribute and each row into a Value (if the row is not an empty value).

List queryResult = GetQueryResult();

//make our hierarchies.
var groups = queryResult
  .GroupBy(row => new {row.id, row.attid})
  .GroupBy(g => g.Key.id);

//now shape each level
List answer =
(
  from typeGroup in groups
  let typeRow = typeGroup.First().First()
  select new Type()
  {
    id = typeRow.id,
    type = typeRow.type,
    Attributes =
    (
      from attGroup in typeGroup
      let attRow = attGroup.First()
      select new Attribute()
      {
        id = attRow.attid,
        label = attRow.label
        Values =
        (
          from row in attRow
          where row.attvalueid.HasValue  //if no values, then we get an empty array
          select new Value() {id = row.attvalueid, value = row.value }
        ).ToArray()
      }
    ).ToArray()
  }
).ToList();