正确的Join/GroupJoin实现

TableA 和 TableB 数据映射如下:

class MyDataContext : DataContext
{
    public Table<tblA> TableA;
    public Table<tblB> TableB;
}

表 作为我的主表并希望加入一个字段, CustomerID 表B 检索 [TableB].[LastName] .

here ,我模仿@tvanfosson的建议:

// appropriately rewritten for my needs - so I thought...
private static IQueryable GetRecordsByView1(IQueryable<tblA> source)
{
    var records = source.GroupJoin(myContext.TableB,
                  info => info.CustomerID,
                  owner => owner.CustomerID,
                  (info, owner) => new
                  {
                      info.CustomerID,
                      Owner = owner.Select(o => o.LastName).DefaultIfEmpty(),
                      Store = info.Store,
                  })
                  .Select(record => new
                  {
                      record.CustomerID,
                      record.Owner,
                      record.Store,
                  });

    return records;
}

source 是动态的,因此一个方法生成动态查询:

public static void QueryStores()
{
    IQueryable<tblA> source = myContext.TableA;

    if (criteriaA)
        source = source.Where(// something);

    if (criteriaB)
        source = source.Where(// something);

    // after processing criteria logic, determine type of view
    switch (byView)
    {
        case View1:
        {
            source = GetRecordsByView1(source);
            break;
        }

        //other case blocks
    }

    myGridView.DataSource = source;
}

无法格式化节点“OptionalValue” 作为SQL执行。

我相信这是在下面的代码行中:

Owner = owner.Select(o => o.LastName).DefaultIfEmpty()

GroupJoin 作为一种扩展方法。