EF Core 2.1 Query - LEFT JOIN

c# ef-core-2.0 entity-framework-core


I am trying to select the equivalent of

SELECT u.NodeId, 
       gtu.GroupId as ParentGroupId
FROM Unit u
LEFT JOIN GroupToUnit gtu ON u.NodeId = gtu.NodeId
JOIN Organisation o ON u.OrgCode = o.OrgCode

My c# equivalent is

IList<OrgChartNode> unitNodes = _db.Units
                                    .Where(u => u.OrgCode.Equals(OrgCode))
                                    .Select(u => new OrgChartNode
                                         Id = u.NodeId,
                                         Name = u.Name,
                                         TierId = 0,
                                         ParentGroupId = u.GroupLinks.First().GroupId,
                                         OrgName = u.Organisation.Name,
                                         OrgCode = u.OrgCode,
                                         ContactName = null,
                                         ContactEmail = null,
                                         ContactPhone = null,
                                         ContactId = null,
                                    .OrderBy(u => u.Name)

This is translating as an initial query for the Units...

Microsoft.EntityFrameworkCore.Database.Command:Information: Executed DbCommand (5ms) [Parameters=[@__OrgCode_0='?' (Size = 5)], CommandType='Text', CommandTimeout='30']
SELECT [u].[NodeId] AS [Id0], [u].[ID] AS [Name0], [u.Organisation].[Name] AS [OrgName], [u].[OrgCode]
FROM [Report_Unit] AS [u]
INNER JOIN [Report_Organisation] AS [u.Organisation] ON [u].[OrgCode] = [u.Organisation].[OrgCode]
WHERE [u].[OrgCode] = @__OrgCode_0
ORDER BY [Name0]

and then a subquery for each Unit to determine its GroupId. (Repeat per record)

Microsoft.EntityFrameworkCore.Database.Command:Information: Executed DbCommand (1ms) [Parameters=[@_outer_NodeId='?' (DbType = Int32)], CommandType='Text', CommandTimeout='30']
SELECT TOP(1) [r1].[GroupId]
FROM [Report_Link_Group_to_Unit] AS [r1]
WHERE @_outer_NodeId = [r1].[NodeId]

It's also failing if the Unit isn't linked.

How do I modify my query to return the expected results? I expect all units, with a null in ParentGroupId if not link. Additionally, what's a good resource to read for learning this syntax? Finding a lot of previous version examples that aren't quite valid.

6/1/2018 12:37:01 AM

Accepted Answer

I was eventually able to get this working using a view in the database linked to an EF class. The problems I had with this earlier were due to my leaving off the {get; set;} in my initial class definition.

public class OrgChartNode
    public int Id { get; set; }

    public string Name { get; set; }

    [Range(0, 6)]
    public int TierId { get; set; }

    public int? ParentGroupId { get; set; }

    public string OrgName { get; set; }

    public string OrgCode { get; set; }

    public string ContactName { get; set; }

    public string ContactEmail { get; set; }

    public string ContactPhone { get; set; }

    public int? ContactId { get; set; }

    public int? GroupTypeId { get; set; }


Then in the DBContext

protected override void OnModelCreating(ModelBuilder builder)

And finally, loading data and converting to JSON

public JsonResult OnGet(string OrgCode)
    OrgChartNodes = _db.OrgChartNodes
                    .Where(g => g.OrgCode.Equals(OrgCode))

    return new JsonResult(OrgChartNodes);
7/16/2018 11:01:34 PM

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