"deko" wrote:

> When I define a DataTable's primary key, do I need to set it as unique and
> to disallow nulls?
>
>    project_ID.Unique = true;
>    project_ID.AllowDBNull = false;
>
> Or is this all that's necessary:
>
>    tblProject.PrimaryKey = new DataColumn[] {
> tblProject.Columns["project_ID"] };
>
> Should I set just the PK or do I need the other two lines of code as well?
>
>
>
>

"deko" wrote:

> > Once you define a DataColumn as primary key column, it's Unique becomes true
> > and AllowDBNull becomes false automatically.
>
> Thanks, I was playing around and this indeed appears to be the case.  However, I
> am still having problems trying to delete a row from my DataSet.
>
> Here is the DataTable definition:
>
> DataTable tblProject = database.Tables.Add("TableProject");
> tblProject.Columns.Add("ProjectName", typeof(string));
> [more columns added...]
> //primary key definition
> DataColumn project_ID = tblProject.Columns.Add("Project_ID", typeof(Int32));
> tblProject.PrimaryKey = new DataColumn[] { tblProject.Columns["Project_ID"] };
> project_ID.AutoIncrement = true;
> project_ID.AutoIncrementSeed = 1;
> project_ID.AutoIncrementStep = 1;
>
> Here is how I am trying to delete the row:
>
> [drPrj is a DataRow object]
> if (drPrj != null)
> {
>    drPrj.Delete();
>    dtPrj.AcceptChanges();
> }
>
> This results in an apparent key violation - "Project_ID cannot be null"
> "TableProject" is the parent table and "TableConfiguration" is the child table.
>
> Here is the FK definition:
>
> DataColumn parentCol =
>    database.Tables["TableProject"].Columns["Project_ID"];
> DataColumn childCol =
>    database.Tables["TableConfiguration"].Columns["Project_ID"];
> ForeignKeyConstraint fkPC =
>    new ForeignKeyConstraint("ProjectConfigurationFK", parentCol, childCol);
> fkPC.DeleteRule = Rule.Cascade;
> fkPC.AcceptRejectRule = AcceptRejectRule.Cascade;
> database.Tables["TableConfiguration"].Constraints.Add(fkPC);
>
> If you see anything wrong here, please let me know...
>
> Why am I getting that error?
>
> Full text of error:
>
> System.Data.NoNullAllowedException was unhandled
>   Message="Column 'Project_ID' does not allow nulls."
>   Source="System.Data"
>
> Thanks in advance.
>
>
>
>

"deko" wrote:

> > if (drPrj["Project_ID"] != DBNull.Value)
> > {
> >    drPrj.Delete();
> >    dtPrj.AcceptChanges();
> > }
>
> That sounds like good advice.  Thanks.
>
> One more question about foreign keys:
>
> When I define the table that will contain a foreign key field, should I disallow
> nulls in that field?
>
> For example:
>
> DataTable tblConfiguration = database.Tables.Add("TableConfiguration");
> tblConfiguration.Columns.Add("ConfigurationName", typeof(string));
> tblConfiguration.Columns.Add("Project_ID", typeof(int)); //foreign key
> <<*************
> //primary key definition
> DataColumn Configuration_ID = tblConfiguration.Columns.Add("Configuration_ID",
> typeof(Int32));
> tblConfiguration.PrimaryKey = new DataColumn[] {
> tblConfiguration.Columns["Configuration_ID"] };
> Configuration_ID.AutoIncrement = true;
> Configuration_ID.AutoIncrementSeed = -1;
> Configuration_ID.AutoIncrementStep = -1;
>
> **********>> Should I add this line of code:
>
>  project_ID.AllowDBNull = false;
>
> ???
>
>
>

"deko" <deko@nospam.com> a écrit dans le message de
news:cP-dnUB44dUKaInZnZ2dnUVZ_sGdnZ2d@comcast.com...
> > if (drPrj["Project_ID"] != DBNull.Value)
> > {
> >    drPrj.Delete();
> >    dtPrj.AcceptChanges();
> > }
>
> That sounds like good advice.  Thanks.
>
> One more question about foreign keys:
>
> When I define the table that will contain a foreign key field, should I
disallow
> nulls in that field?
>
> For example:
>
> DataTable tblConfiguration = database.Tables.Add("TableConfiguration");
> tblConfiguration.Columns.Add("ConfigurationName", typeof(string));
> tblConfiguration.Columns.Add("Project_ID", typeof(int)); //foreign key
> <<*************
> //primary key definition
> DataColumn Configuration_ID =

> typeof(Int32));
> tblConfiguration.PrimaryKey = new DataColumn[] {
> tblConfiguration.Columns["Configuration_ID"] };
> Configuration_ID.AutoIncrement = true;
> Configuration_ID.AutoIncrementSeed = -1;
> Configuration_ID.AutoIncrementStep = -1;
>
> **********>> Should I add this line of code:
>
>  project_ID.AllowDBNull = false;
>
> ???
>
>