Some things to avoid when working with EOF. Some of these things are contraindicated in Apple documentation, others are not. But all are things that experience shows EOF does not expect, and can lead to all sorts of trouble, including mysterious exceptions, and EOF getting confused about what changes must be saved to the database.
Don't use an EO's Constructor.Don't set EO properties in the EO constructor - use
From Apple's Documentation:
You may wonder why it's not recommended to initialize an enterprise object's values in an object's constructor. An enterprise object's constructor represents the earliest state in the life of a particular object. The state of an enterprise object at the point of construction is not complete; the object is not fully initialized. It may not yet have been inserted into an editing context and it might not even have been assigned a global ID. You don't ever want to manipulate an enterprise object that isn't in an editing context or that doesn't have a global ID.
Therefore, any logic you add in an enterprise object's constructor may fail or be invalidated while the object finishes initializing. By providing custom logic in awakeFromInsertion or awakeFromFetch, however, you are guaranteed that an enterprise object is fully initialized.
awakeFromInsertion(...)there are two times that this method can be called when the EO being inserted is not actually being initialized for the first time.
- If it's being reinserted to a EC after it was deleted from another or the same EC. Only new EOs will have a temporary GlobalID.
- If it's being saved to the server-side application by a Java Client WebObjects application. These EOs will have been inserted on the client-side and likely already have values set. To avoid overriding these values, you should verify that the attribute's value is null first.
Don't change the value of an attribute in the accessor methodEOF calls those accessor methods many times over the life of the EO. An accessor method is the last place that you want to be making any changes or doing any computations to determine the value. Default values should be set in
awakeFromInsertion(...). If you need to update one attribute (i.e. lastChangedDate) when another attribute (i.e. userName) is changed then implement the
setUserName()method and document that it has the side effect of calling
setLastChangedDate(...). An alternate method if you would need to implement too many set methods or if you're concerned about overhead of calling
setLastChangedDate()too many times is to implement a listener for the editingContextWillSaveChanges notification from the EOEditingContext and call
Always Insert First.Don't do anything to an EO before inserting it into an editing context. Always insert EOs into ECs immediately. See rule #1.
Don't modify any EO properties inDoing this in
validateValueForKey(...)is ok as Chuck Hill noted in the list.
Always invokeIf overriding
superwhen overriding EOF methods
awakeFromInsertion(...), remember to call the superclass implementation. Same with
Don't use EOF in model class static initializersDoing so forces EOF into operational mode before the frameworks are initialized. Use lazy loading of the entity instead.
- Don't use mutable classes (
NSMutableDictionary, or any other class that can change internal state after creation) as attributes. If you want this effect, use immutable classes and provide cover methods to replace the immutable instance with an updated instance. For example:
Always Lock your EditingContextDon't call any EOEditingContext methods, or any methods on an EO in an EOEditingContext without first ensuring that the EOEditingContext is locked. That includes bindings in a WOD. It's your job to make sure the EO's that you bind to in a page are locked.
Project Wonder provides auto-locking, so you don't have to worry about this.