Data member property of datasource cannot be found-CodePudding

I have a Winform to display the contents of two related data tables, EquipReq (the parent) and EqReqItems (the child).

After filling a new data set (DS) with both tables, I add a relation to the data set as follows:

DS.Relations.Add("RItems", DS.Tables("EquipReq").Columns("RecID"), DS.Tables("EqReqItems").Columns("ReqNo"), False)

I bind a new binding source BS as follows:

Dim BS As New BindingSource
BS.DataSource = DS
BS.DataMember = "EquipReq"

I (try) to bind another new binding source BSI as to the added relation RItems as follows:

Dim BSI As New BindingSource
BSI.DataSource = DS
BSI.DataMember = "RItems"

At this last line, I get the error "Data member 'RItems' cannot be found in the data source".

I have iterated through the relations of the data set DS and only one is shown with the name of RItems. I have also double-checked each data table to ensure the named columns in the relation exist in those tables.

Am I overlooking something obvious? What can I do to resolve this issue?

TIA,

Larry

CodePudding user response：

If you are trying to set up parent/child data-binding then the child binding needs to be to the parent BindingSource, not the DataSet. You should add the BindingSources to the form in the designer, so they are accessible throughout the form code. Also, always set the DataSource last.

With parentBindingSource
    .DataMember = "ChildTable"
    .DataSource = myDataSet
End With

With childBindingSource
    .DataMember = "ParentChildRelation"
    .DataSource = parentBindingSource
End With

The reason you should set DataSource last, after DataMember, DisplayMember and ValueMember, is that all the binding is set up when you set the DataSource. If you set it first then all the binding has to be changed when you then set the other property. If you set DataSource last then all the work of setting up the binding is done only once.