Is changing a WCF data member to nullable a breaking change?

Question

I have a WCF Service that is called by the client.

If my current data contract for the return value is:

[Serializable]
[DataContract]
public class StatisticsDto
{
    [DataMember]
    public int EmployeeId { get; set; }
}

and I change only the server implementation to:

[Serializable]
[DataContract]
public class StatisticsDto
{
    [DataMember]
    public int? EmployeeId { get; set; }
}

does this result in incompatibility until I update the client? or is the value automatically cast to int unless it is null?

Answer 1

Agree with commenter @Selvin. It is certainly a breaking change for the client until you update the client to handle null values in EmployeeId field.