The WeakReferenced Abbtribute forces the mapper to use outer joins when joining parent and child table using Virtual Links.
This attribute is always useful if the child property is not a mandatory property of the parent class.
Think about a contact object that has a mandatory firstname and lastname and a salutation enumeration. The salutation enumeration is not mandatory.
/// <summary>
/// Descripes a contact
/// </summary>
[Table("CONTACTS")]
public class Contact : ValueObject
{
private Salutation salutation;
private string salutationText; // get text from db using a virtual link
private string firstName;
private string lastName;
/// <summary>
/// Gets or sets the salutation.
/// </summary>
/// <value>The salutation.</value>
public Salutation Salutation
{
get { return salutation; }
set { salutation = value; }
}
/// <summary>
/// Gets or sets the salutation text.
/// </summary>
/// <value>The salutation text.</value>
[VirtualLink(typeof(SalutationText), "Value", "Key", "Salutation")]
public string SalutationText
{
get { return salutationText; }
set { salutationText = value; }
}
/// <summary>
/// Gets or sets the name of the first.
/// </summary>
/// <value>The name of the first.</value>
[Required]
[PropertyLength(50)]
public string FirstName
{
get { return firstName; }
set { firstName = value; }
}
/// <summary>
/// Gets or sets the name of the last.
/// </summary>
/// <value>The name of the last.</value>
[Required]
[PropertyLength(50)]
public string LastName
{
get { return lastName; }
set { lastName = value; }
}
}
The salutation enumeration looks like this:
/// <summary>
/// Salutation
/// </summary>
public enum Salutation
{
None,
DearMr,
DearMrs,
MyFriend
}
And last but not least, the text corresponding to that enumeration will be retrieved by a virtual link using database joins.
/// <summary>
/// Static texts for salutation
/// </summary>
[StaticData]
[WeakReferenced]
public class SalutationText : ValueObject
{
private Salutation key;
private string value;
public Salutation Key
{
get { return key; }
set { key = value; }
}
public string Value
{
get { return value; }
set { this.value = value; }
}
}
When selecting the contact the SQL looks like that:
SELECT contacts.*, v1.VALUE AS salutationtext
FROM contacts LEFT OUTER JOIN salutationtext v1 ON contacts.salutation = v1.KEY
If you wouldn’t use the attribute [WeakReferenced] a contact without a filled salutation could not be loaded.
Because of that issue the attribute is very important.
Loading ...