Left outer join of datatable with linq expression?

I have two DataTables:

DataTable dtFields = new DataTable("tmpFieldTable");
 
             dtFields.Columns.Add("FieldID");
             dtFields.Columns.Add("CDGroupID");
             dtFields.Columns.Add("CDCaption");
             dtFields.Columns.Add("fldIndex");
 

and

 DataTable dtCDGroup = new DataTable("tmpCDGroup");
 
             dtCDGroup.Columns.Add("CDGroupID");
             dtCDGroup.Columns.Add("Name");
             dtCDGroup.Columns.Add("Priority");
 

I am using following LINQ expression to join these tables:

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);
 

How can I perform left outer join with these DataTables?

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