HOW TO: Avoide “Cannot create a child list for field …..”
From: Burton G. Wilkins (BurtonGWilkins_at_discussions.microsoft.com)
Date: 07/23/04
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Date: Fri, 23 Jul 2004 07:57:07 -0700
Dear ADO.Net community:
I entered this question last night but now I can't find it this morning. I hope I am not creating double entried.
As an object, I am trying to develop some ADO.Net code which would process a relational SLQ query on a variety of SQL platforms. The code I have succeeds with Microsoft SQL and Microsoft Access, but then fails for Oracle and IBM DB2. My question is, what I am I missing that would ensure performance for all platforms. The error I am getting from Oracle and DB2 are the same “Cannot create a child list for field …..” , so I suspect if I can solve one, then both will work. Please advise what’s missing.
For example, the following two approaches fail in Oracle when I try and run it through ADO.Net:
SELECT
A.EMPNO,
A.ENAME,
B.DNAME
FROM
(SCOTT.EMP A
INNER JOIN SCOTT.DEPT B ON
B.DEPTNO = A.DEPTNO)
.. or
SELECT
A.EMPNO,
A.ENAME,
B.DNAME
FROM
(SCOTT.EMP A
INNER JOIN SCOTT.DEPT B ON
B.DEPTNO = A.DEPTNO)
Here in general is how I am trying to return the result.
(1) Creates a Connection:
Dim mconConnection As OracleClient.OracleConnection
Dim mstrConnecion = “Data Source=WORD;User ID=SCOTT;Password=TIGER;”
mconConnection = New OracleClient.OracleConnection()
mconConnection.ConnectionString = mstrConnection
(2) Create a Data Adapter:
Dim mdaDataAdapter As OracleClient.OracleDataAdapter
Dim mstrSelect As String
mstrSelect = “strSelect = "SELECT A.EMPNO, A.ENAME, B.DNAME FROM (SCOTT.EMP A INNER JOIN SCOTT.DEPT B ON B.DEPTNO = A.DEPTNO)
mdaDataAdapter = New OracleClient.OracleDataAdapter()
mdaDataAdapter.SelectCommand = New
OracleClient.OracleCommand(mstrSelect, mconConnection)
(3) Create a Data Table:
mdtDataTable = New DataTable("(SCOTT.EMP")
mdcA_EMPNO = New DataColumn()
mdcA_EMPNO.ColumnName = "A.EMPNO"
mdcA_EMPNO.DataType = System.Type.GetType("System.Decimal")
mdcA_EMPNO.AutoIncrement = False
mdcA_EMPNO.Caption = "A.EMPNO”
mdcA_EMPNO.ReadOnly = False
mdcA_EMPNO.Unique = False
mdtDataTable.Columns.Add(mdcA_EMPNO)
mdcA_ENAME = New DataColumn()
mdcA_ENAME.ColumnName = "A.ENAME"
mdcA_ENAME.DataType = System.Type.GetType("System.String")
mdcA_ENAME.AutoIncrement = False
mdcA_ENAME.Caption = "A.ENAME"
mdcA_ENAME.ReadOnly = False
mdcA_ENAME.Unique = False
mdcA_ENAME.MaxLength = 10
mdtDataTable.Columns.Add(mdcA_ENAME)
mdcB_DNAME = New DataColumn()
mdcB_DNAME.ColumnName = "B.DNAME"
mdcB_DNAME.DataType = System.Type.GetType("System.String")
mdcB_DNAME.AutoIncrement = False
mdcB_DNAME.Caption = "B.DNAME"
mdcB_DNAME.ReadOnly = False
mdcB_DNAME.Unique = False
mdcB_DNAME.MaxLength = 9
mdtDataTable.Columns.Add(mdcB_DNAME)
(4) Establish Table Mapping and Set Command String:
Dim mTableMap As DataTableMapping
mTableMap = mdaDataAdapter.TableMappings.Add("Table", "(SCOTT.EMP")
mTableMap.ColumnMappings.Add("A.EMPNO", "A.EMPNO")
mTableMap.ColumnMappings.Add("A.ENAME", "A.ENAME")
mTableMap.ColumnMappings.Add("B.DNAME", "B.DNAME")
mdaDataAdapter.SelectCommand.Connection.ConnectionString= mstrConnection
(5) Define Command Object
Dim cmdCommand As New OracleClient.OracleCommand()
cmdCommand.Connection = mconConnection
mconConnection.Open() 'Open the connection.
cmdCommand.CommandType = CommandType.Text
cmdCommand.CommandText = mstrSelect
(6) Create and fill the Data Adapter:
Dim mdaDataAdapter As OracleClient.OracleDataAdapter
Dim mdsDataSet As DataSet
mdsDataSet = New DataSet()
mdaDataAdapter.SelectCommand = cmdCommand
mdaDataAdapter.Fill(mdsDataSet, "(SCOTT.EMP")
(7) Get Record Count: (This is where the failure occurs.)
mintRecordCount = Form.BindingContext(mdsDataSet, "(SCOTT.EMP").Count
When this last instruction is exercised, both Oracle and DB2 exception out returning the “Cannot create a child list for field SCOTT” message. Microsoft Access and SQL do not error out.
So my question to all is this. What should I add to these approaches so that the ADO.Net code will not to exception out? Please offer a few lines of code.
I would very much appreciate your comments to this question. Thank you for reading this explanation and considering this request.
Sincerely,
Burton G. Wilkins.
- Next message: Paul Clement: "Re: Want binary data to show up as "Bitmap Image" with access/ado"
- Previous message: Heewa: "Certain fields not updatable"
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