[英]Left outer join of datatable with linq expression?
我有兩個DataTable
:
DataTable dtFields = new DataTable("tmpFieldTable");
dtFields.Columns.Add("FieldID");
dtFields.Columns.Add("CDGroupID");
dtFields.Columns.Add("CDCaption");
dtFields.Columns.Add("fldIndex");
和
DataTable dtCDGroup = new DataTable("tmpCDGroup");
dtCDGroup.Columns.Add("CDGroupID");
dtCDGroup.Columns.Add("Name");
dtCDGroup.Columns.Add("Priority");
我正在使用以下LINQ表達式來聯接這些表:
var resultList = dtFields.AsEnumerable()
.Join(dtCDGroup.AsEnumerable(),
fieldList => fieldList.Field<string>("CDGroupID"),
cd => cd.Field<string>("CDGroupID"),
(fieldList, cd) => new
{
FieldID = fieldList.Field<string>("FieldID"),
CdGroup = cd.Field<string>("Name"),
CDCaption = fieldList.Field<string>("CDCaption"),
Priority = (cd.Field<string>("Priority") ?? "99"),
fldIndex = fieldList.Field<string>("fldIndex").ToString()
})
.OrderBy(result => result.Priority)
.ThenBy(result => result.fldIndex);
如何使用這些DataTable
執行左外部DataTable
?
左聯接不是本地使用lambda表達式提供的。 但是您可以使用GroupJoin和SelectMany方法來實現。
var result = new string[] { "A", "B" }.GroupJoin(new string[] { "B" }, l => l, r => r, (l, r) => new { l, r }).ToList();
Console.WriteLine(result.Count());
這將導致result [0] .r.Count()= 0和result [1] .r.Count()= 1。
希望這會有所幫助。
問候。
只需將DefaultIfEmpty()
添加到表中:
resultList = dtFields.AsEnumerable()
.Join(dtCDGroup.AsEnumerable().DefaultIfEmpty(),
fieldList => fieldList.Field<string>("CDGroupID"),
cd => cd.Field<string>("CDGroupID"),
(fieldList, cd) => new
{
FieldID = fieldList.Field<string>("FieldID"),
CdGroup = cd.Field<string>("Name"),
CDCaption = fieldList.Field<string>("CDCaption"),
Priority = (cd.Field<string>("Priority") ?? "99"),
fldIndex = fieldList.Field<string>("fldIndex").ToString()
})
.OrderBy(result => result.Priority)
.ThenBy(result => result.fldIndex);
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