Using Nullable TypesΒΆ

When synchronizing data, it is important that you understand the values being read and being written. One scenario that you must consider carefully is when you are reading nullable types.

Consider a case where you are mapping data from a contact in xDB to a contact in Dynamics CRM. In xDB, the contact has a property on a facet that represents the contact’s date of birth.

On the contact facet, the date of birth is defined as DateTime?, which is a nullable DateTime. This makes it possible for no date of birth to be specified (meaning the property is null).

As a developer, when you work with nullable type values, you use them the same way you use value types. For example:

DateTime? now = DateTime.Now;
if (now > new DateTime(2017, 1, 1))
    //do something

But a more accurate view of what is going on is the following, because this more closely reflects the code after it is compiled:

DateTime? now = new DateTime?(DateTime.Now);
if (now.Value > new DateTime(2017, 1, 1))
    //do something

This has a significant impact within Data Exchange Framework. The framework uses reflection for most of its mapping operations. Reflection works on the compiled code, not the source code.

This means that when you are using nullable types with framework components, you must use the Value property.

So, to continue the example, if you want to use the xDB contact’s date of birth as a source value in a mapping, you cannot simply point to the property on the contact facet. That will give you access to a DateTime?. You must read the Value property from the DateTime? object.

The field “Source Value Transformer” on the Value Mapping template was designed for this situation.

  1. In Content Editor, select your tenant.
  2. Navigate to Data Access > Value Readers > Common.
  3. Create a new item using the template Property Value Reader.
  4. Select the new item.
  5. For the field Property Name, set the value to be “Value”.
  6. Save the item.
  7. Navigate to the Value Mapping item that represents the mapping of the xDB date to the CRM date.
  8. For the field Source Value Transformer, select the item you created in step 3.
  9. Save the item.