Validate Objects

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eXpress Persistent Objects has no built-in validation logic. You can override the IXPObject.OnSaving or IXPObject.OnDeleting method to implement validation logic. This can be useful, for instance, to perform various checks when implementing 'defensive programming'. It's not recommended to mix the process of saving an object with the business logic.

The following example demonstrates how to prevent the Name property from being set to an empty string. If this property is set to an empty string, XPO throws a RequiredPropertyValueMissing exception.

public class RequiredPropertyValueMissing: Exception {
    public RequiredPropertyValueMissing(XPObject theObject, string propertyName):
        base(String.Format("The {0} property of the {1} object with id {2} must have a value", 
          propertyName, theObject.GetType().Name, theObject.Oid)) {

public class Company : Person {
public string Name {
    get { return fName; }
    set { SetPropertyValue(nameof(Name), ref fName, value); }
string fName = "";

    protected override void OnSaving() {
        if (Name == "")
          throw new RequiredPropertyValueMissing(this, nameof(Name));
See Also