Constraint on DataColumn in C# DataTable?

Question

is it possible to create a value range constraint on a DataTable in C#?

I'm dynamically adding a column to a DataTable:

this.PrimaryCorrelationMatrix.Columns.Add(sName, typeof(int));

but I'd like all values within this Column to be integers from [0, 10]. Can I implement such a constraint directly on the DataTable?

The next best option I can think of is to create some object with possible values [0, 10], and instead of typeof(int), using typeof(specialObj).

Answer 1

One way to do this is to inspect the e.ProposedValue in the ColumnChanging event of the DataTable.

To have the constraint on a particular column, you can use the ExtendedProperties collection of the DataColumn to act as your flag to check those constraints:

DataTable dt = new DataTable();
DataColumn dc = new DataColumn("Range", typeof(int));
dc.ExtendedProperties.Add("Min", 0);
dc.ExtendedProperties.Add("Max", 10);
dt.Columns.Add(dc);
dt.ColumnChanging += dt_ColumnChanging;

In the ColumnChanging event, you would check if those properties exist, then use them:

void dt_ColumnChanging(object sender, DataColumnChangeEventArgs e) {
  if (e.Column.ExtendedProperties.ContainsKey("Min") &&
      e.Column.ExtendedProperties.ContainsKey("Max")) {
    int min = (int)e.Column.ExtendedProperties["Min"];
    int max = (int)e.Column.ExtendedProperties["Max"];
    if ((int)e.ProposedValue < min) e.ProposedValue = min;
    if ((int)e.ProposedValue > max) e.ProposedValue = max;
  }
}

Answer 2

I can recommend you to forget about data tables and use classes. You can use data annotation to validate your model.

Use this attribute to validate a range of values for an specific property/

This code is extracted from the specified article(example of class making the validation of a range):

public class Product
{

  [Range(5, 50)]
  public int ReorderLevel { get; set; }

  [Range(typeof(Decimal),"5", "5000")]
  public decimal ListPrice { get; set; }

}

Your are going to find a lot of benefits of using classes.

Answer 3

This is an old post but I am using a solution to sync the Check_Constraints NOT filled by the OleDbDataAdapter.FillSchema on Access Databases worth to mention. Just used a OleDbConnection to retrieve GetOleDbSchemaTable and foreach() the rows extracting the validation text expression and created an anonymous delegate at the appropriate Table & Column attached to the proper Table.ColumnChanging event. The string validation provided by the Access schema will then be evaluated dynamically by the handy Eval() function described here . There is my code:

DataTable schemaTable = connection.GetOleDbSchemaTable(OleDbSchemaGuid.Check_Constraints, null);
// Attach delegate Eval() of each Check_Constraints on proper Table/Column
foreach (DataRow myField in schemaTable.Rows)
{
    string constraint_name = "";
    string check_clause = "";
    foreach (DataColumn myProperty in schemaTable.Columns)
    {
        if (myProperty.ColumnName == "CONSTRAINT_NAME")
            constraint_name = myField[myProperty.ColumnName].ToString();
        if (myProperty.ColumnName == "CHECK_CLAUSE")
            check_clause = myField[myProperty.ColumnName].ToString();
    }
    var rule = constraint_name.Replace("[", "").Replace("]", "").Split('.');
    if (rule.Length == 3 && dataset.Tables.Contains(rule[0]) && dataset.Tables[rule[0]].Columns.Contains(rule[1]) && String.IsNullOrEmpty(check_clause) == false)
    {
        dataset.Tables[rule[0]].ColumnChanging += delegate (object sender, DataColumnChangeEventArgs e)
        {
            if (e.Column.ColumnName == rule[1] && Convert.ToBoolean(ToolBox.Eval(e.ProposedValue + check_clause)) == false)
            {
                throw new Exception("Tabela: " + rule[0] + ", coluna: " + rule[0] + ", cheque: " + check_clause);
            }
        };
        Debug.WriteLine(rule[0] + "." + rule[1] + ": " + check_clause);
    }
}