I am having trouble in setting primary key for a datatable with existing column. I am getting this exception
These columns don't currently have unique values.
The code I am using for the same is like,
dtTemp.PrimaryKey = New DataColumn() {dtTemp.Columns("mycolumn")}
where mycolumn is an existing column in datatable dtTemp with rows like
501,502,503,...901,902,903
(doesn't have unique values)
Note:
The same code with same random values in datatable column works well in one of the similar projects. Any directions would be helpful.
try setting the EnforceConstraints property to False
example -
dtTemp.EnforceConstraints = False
dtTemp.PrimaryKey = New DataColumn() {dtTemp.Columns("mycolumn")}
Related
I am trying to update my SQL database with the code provided, I am basically trying to take a select statement to bring back just the INTGenderID based on a combo box and make it equal to a string then convert that to an integer when I do my update back into my database. If you need more info let me know. The main table is TGolfers and the parent table is TGenders.
I think I understand the question. Let's assume that you have a database table named Thing and that has columns ThingId and Name. You would generally query the database to populate a DataTable and then bind that to your ComboBox, e.g.
Dim table As New DataTable
Using connection As New OleDbConnection(connectionString),
command As New OleDbCommand("SELECT ThingId, Name FROM Thing", connection)
connection.Open()
Using reader = command.ExecuteReader()
table.Load(reader)
End Using
End Using
With thingComboBox
.DisplayMember = "Name"
.ValueMember = "ThingId"
.DataSource = table
End With
The user will now see a list of Name values in the ComboBox and, when they select one, you can get the corresponding ThingId from the SelectedValue property, e.g.
Dim thingId = CInt(thingComboBox.SelectedValue)
Below I load a dataset, which I believe is table 0. Then I set the name of table 0 in the dataset to PickTable:
PickDataSet.ReadXml(My.Computer.FileSystem.SpecialDirectories.MyDocuments & Pickfile)
PickDataSet.Tables(0).TableName = "PickTable"
I'm having trouble now finding syntax to set the primary key for the PickTable. Column 0 is unique and always has a value. I need to make this the primary key.
I tried something like this:
PickDataSet.Tables("PickTable").PrimaryKey = PickDataSet.Tables("PickTable").Columns(0);
The .PrimaryKey property of DataTable expect an array of DataColumn objects. So you can set the first column as primary key with the following line:
PickDataSet.Tables("PickTable").PrimaryKey = {PickDataSet.Tables("PickTable").Columns(0)}
'or
PickDataSet.Tables("PickTable").PrimaryKey = New DataColumn() {PickDataSet.Tables("PickTable").Columns(0)}
I am developing a simple savings account application where I am able to simulate deposit, withdrawal and transfer of money. I have a button called "Deposit" that I can click and data will be recorded in my database.
To make that insert statement I am using SQL parameters and this is the code:
SqlCon = New SqlConnection
SqlCon.ConnectionString = "............"
Try
Query = "INSERT INTO Transacoes(tpAccount, dateTransaction, descrTransaction, amoutTransaction, balanceTransaction)
VALUES(#tpAccount, #dateTransaction, #ddescrTransaction, #amoutTransaction, #balanceTransaction)"
SqlCon.Open()
SqlCmd = New SqlCommand(Query, SqlCon)
With SqlCmd.Parameters
.Add("#tpAccount", SqlDbType.Char).Value = cbTipoConta.Text
.Add("#dateTransaction", SqlDbType.DateTime).Value = txtDate.Text
.Add("#descrTransaction", SqlDbType.Char).Value = cmdDepositar.Text
.Add("#amoutTransaction", SqlDbType.Int).Value = txtDeposito.Text
.Add("#balanceTransaction", SqlDbType.Int).Value = txtBalance.Text
End With
SqlCmd.ExecuteNonQuery()
SqlCon.Close()
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
In this table I have an "ID" column but I don't want it to display on SQL parameters and shows me an error:
Cannot insert the value NULL into column 'Id'`.
I should autoincrement the Id and then this will work fine? Or what is the best way to solve this?
You should autoincrement the ID, I always use ID column with Identity(1,1) even though it is not needed at the moment. It is always nice to select specific row fast and when the ID is autoincremented, then you have only one where condition.
In order to be able to omit the ID field in your insert statement you need to set an auto increment (identity) on that field.
REF: https://technet.microsoft.com/en-gb/library/ms188263(v=sql.105).aspx
Identity is not the only solution in this case. The other one is named sequence.
In your case you can simply create a new sequence like in this example
create sequence dbo.id_sequence as int
start with 0
increment by 1;
More information about create of sequence you can find here
If you have a sequence you can use it as a defalut value for any column in table what you can see in example on point D here. You can even use more sequences to work with more than one column in a table if you want.
Difference between identinty and sequence is that you can use an identity only for one column (with sequence or even sequences you can do it with many columns in one table) and for set identity you need to recreate table (the alter is not allowed in this case) or remove column with identity and create a new one with it (and you need to be aware about constraints and relations with deleted column). With sequences you can simply alter the table in any moment with any column you need.
With sequences you can update or insert a value to a column (with identity you can't) so if you use this part of your work to simulate something it colud be a good idea to make a possibility of using original ids (if you need it of course) instead of that created by identity.
I'm trying to progress my programming abilities by coding in Visual Basic forms. I've created a database and linked that to a VB form, I'm now coding a way to write into the database instead of reading.
I'm filling an array which is in-turn put into the dataset row by row however when attempting to 'update' the table adapter I get the following error:
Update requires a valid UpdateCommand when passed DataRow collection with modified rows.
I believe this has something to do with primary keys, the table that my adapter is updating does NOT have a primary key as it's involved in a relationship with another table, containing a primary key. How can I update my table adapter without getting this error? Thanks.
The error message you've mentioned has nothing to do with primary keys on the table you are attempting to update, instead it's complaining because you haven't given your adapter a valid command which it can use to update the underlying table.
You'd hit the same error if you attempted to insert or delete new rows without specifying an insert or delete command on your adapter.
To solve the problem, initialise your UpdateCommand property to something meaningful, for example:
'Open connection
Using Conn as new OleDbConnection("connection string")
'This is the command that will update your table in the database
Using UpdateCmd = Conn.CreateCommand()
UpdateCmd.CommandText = "update yourtable set col1 = ?, col2 = ?"
'Create a parameter to pass in the value of the "col1" column on "yourtable"
Dim ColOneParam = UpdateCmd.Parameters.Add("#Col1", OleDbType.Integer)
ColOneParam.SourceColumn = "Name of column in DataTable which corresponds to col1"
'Create a parameter to pass in the value of the "col2" column on "yourtable"
Dim ColTwoParam = UpdateCmd.Parameters.Add("#Col2", OleDbType.Integer)
ColTwoParam.SourceColumn = "Name of column in DataTable which corresponds to col2"
'Data adapter which will perform the specified update command for each
'newly inserted row
Using Adapter As New OleDbDataAdapter
'Set the update command on the adapter, if you omit this line you'll
'encounter the original error you mentioned
Adapter.UpdateCommand = UpdateCmd
'This is the data table containing the rows you wish to update
Dim NewRows As New DataTable("SomeTable")
'For each modified row in NewRows, update it in the database
Adapter.Update(NewRows)
End Using
End Using
End Using
The above code assumes a table in the database called yourtable with two columns col1 and col2 which are numeric.
The Using blocks simply ensure that the database objects are properly disposed off so you don't end up leaking resources.
I am hitting an MS Access db with VB2005 and I am creating a table object like this
Dim sSQL As String = "SELECT * FROM tblCars WHERE WeekOf=#6/1/2011#"
Dim da As New OleDb.OleDbDataAdapter(sSQL, conn)
Dim ds As New DataSet
da.Fill(ds, "CarData")
Dim cb As New OleDb.OleDbCommandBuilder(da)
The table should have no rows since the data is brand new. I read a data text file with new data and pump this data into the table and add new rows like so:
'create a new empty row
Dim dsNewRow As DataRow = ds.Tables("CarData").NewRow()
'update the new row with fresh data
dsNewRow.Item("DriveDate") = dd
dsNewRow.Item("DCode") = dc
dsNewRow.Item("CarNum") = carID
'about 15 more fields
'add the filled row to the DataSet table
ds.Tables("CarData").Rows.Add(dsNewRow)
'end loop
'update the database with the new rows
da.Update(ds, "CarData")
The table in the db has no primary keys but all this works and i get all my new data inserted into the Data table tblCars.
Now it so happens that I must also account for cars with no data. For that my plan was to get a list of cars from the control table and merge it with the Data table.
Dim sSQL As String = "SELECT CarId FROM tblControlCars WHERE ActiveCar=True;"
Dim daAct As New OleDb.OleDbDataAdapter(sSQL, conn)
Dim ds As New DataSet
daTail.Fill(ds, "ActCars")
Dim cbAct As New OleDb.OleDbCommandBuilder(daAct)
I then create my primary keys for the tables and then merge them.
ds.Tables("CarData").Merge(ds.Tables("ActCars"))
This will give me a table with all the new data for cars that do have data and also a place holder for those cars that are active but did not get any data. However, when I try to do an update back to the db I get an error
System.InvalidOperationException: Dynamic SQL generation for the UpdateCommand is not supported against a SelectCommand that does not return any key column information.
I'm not sure I understand why the Merged data is not able to be pushed to the database.
I've had the same problem before just add a primary key in your database table , the command builder needs a unique identification field to generate a proper command .
You can simply create a field called "id" and make auto-number then you don't have to update it manually and make it a primary key that's it