Core data predicate relationship swift

ios - Core Data NSPredicate fetch on entity relationship using in clause - Stack Overflow

core data predicate relationship swift

Predicates are one of the most powerful features of Core Data, but they are a predicate is a filter: you specify the criteria you want to match, and Core Data will . Core data is used to manage the model layer object in our data changes, adding Predicates and complex relationships od databases. As you. Explains how to manage objects using the Core Data framework. Core Data does not let you create relationships that cross stores. Swift. class EmployeeMO: NSManagedObject {; @NSManaged address: AAAAddressMO? } . (The fetch request typically uses a predicate to constrain the result.).

Build and run, and you should see an empty table view, as follows: Now you can set about making it possible for users to add data as they see fit. One will be used to add a new bank, and the other will show the search view.

You create an instance of FailedBankInfo and you populate the properties with values. Finally, you save the context to make sure the insertion is committed to the database.

Core Data on iOS 5 Tutorial: How To Work with Relations and Predicates |

If you run the application now, you should notice that the table view gets updated correctly with the new instance without requiring a call to reloadData.

This is due to the these functions, both inherited from previous versions of the project: This takes care of four possible changes to the table view: You can enable that by adding the swipe-to-delete functionality, built-in to table views. You just need to add two methods. The first new method simply indicates which cells in the table are editable. You can either add the following code below tableView: Again, there is a commented-out section of code for this, but instead of using it, replace that code with the following: Build and run, add a few banks, and swipe one of the cells to show the delete button.

Also make sure that a XIB is generated. The view will be pushed by a view controller, so you might want to visualize the space taken by a navigation bar. This will be displayed when necessary via code to edit dates. For the moment, place the picker outside of the visible area of the view.

The Y of the picker should be set to With the picker selected, switch to the Size Inspector tab on the right sidebar and set its position as follows: Add it below the existing initWithNibName: The operation in this case is easy: Add the code for it to the end of the file but before the final end: Add it to the end of the file: Add the necessary code again to the end of the file: Add the following code below viewDidLoad: Add the code for those to the end of the file: Before showing the date picker, the first responder for all text fields is resigned, thus effectively dismissing the keyboard if it was visible.

To test your new view, you need to push it onto the navigation stack when a cell is tapped. Run the app and create a few instances of banks.

Each bank record is editable, including the close date. To save data, hit the save button; to discard changes, just tap the back button. Notice that the date picker and the keyboard never obstruct each other. Changes are reflected in the list of banks with no need to refresh the table view. Think of the classic example of employees and departments — an employee is said to belong to a department, and a department has employees.

In database modeling, relationships can be of three types: This property is usually referred to as cardinality. In the example from the previous section, there is already a relation modeled in Core Data: This is a one-to-one relationship: The graphical view stresses this point by connecting the two entities with one single arrow line. In other words, these two only have eyes for each other.

This is just a string identifying the name of the relation. This is the target or the destination class of the relation. The answer to the question: Is the destination a single object or not? If yes, the relation is of type to-one, otherwise it is a to-many. The definition of the inverse function.

It is pretty rare to find a domain where this is not needed. It is also a sort of logical necessity: In your example, a department can have more than one employee, so this is a to-many relation.

As a general rule, a one-to-many relation has a many-to-one inverse.

Core Data Programming Guide: Fetching Objects

In case you want to define a many-to-many relationship, you simply define one relation as to-many and its inverse as a to-many as well. Make sure you define an inverse for each relationship, since Core Data exploits this information to check the consistency of the object graph whenever a change is made.

This defines the behavior of the application when the source object of a relationship is deleted. For the delete rule in 5 above, there are four possible values: Nullify is the simplest option.

Examples of using NSPredicate to filter NSFetchRequest

They just keep thinking they have not been fired: If you select cascade as the delete rule, then when you delete the source object it also deletes the destination object s. Such a rule is appropriate only if you want to close a department and fire all of its employees as well. In this case it is enough to set the delete rule for department to cascade and delete that department record.

core data predicate relationship swift

Deny, on the other hand, prevents accidental deletions. Delete rules have to be specified for both sides of a relationship, from employee to department and vice versa. Each domain implements its own business logic, so there is no general recipe for setting delete rules.

core data predicate relationship swift

Just remember to pay attention when using the cascade rule, since it could result in unexpected consequences. To maximize the performance of your application, remember this when you devise your data model and try to use relationships only if necessary.

The first step is to add a new entity. The delete rule is the default, nullify 4. As above, this is a to-many relationship 3 with a delete rule of nullify.

core data predicate relationship swift

A new class, named Tag, will pop up in your project tree. Sometimes, quite often, in fact: If this happens to you, select one set of instances and delete them, but choose to remove references rather than to trash the files. At this point, you have changed the Core Data model, so your app will not be compatible with the old model on your device. This new view controller will facilitate the creation of new tags and associating them to a bank details object.

Remember to check the box to create the accompanying XIB file. The users of your application expect more from you, though. Sorting records is a common task. To sort the records returned by the fetch request, we add a sort descriptor, an instance of the NSSortDescriptor class. We initialize it by invoking its init key: We then set the sortDescriptors property of the fetch request.

The sortDescriptors property is of type [NSSortDescriptor], which means we can combine multiple sort descriptors. The order of the sort descriptors determines in which order the sort descriptors are applied. We execute the fetch request and print the names of the records to the console.

core data predicate relationship swift

Home Leisure Work Predicates We can use predicates to refine the result of a fetch request. Predicates, instances of the NSPredicate class, enable us to specify which records we are interested in. Update the previous example as shown below. The syntax of the predicate is reminiscent of SQL.

The [c] specifier indicates that the case of the letter o should be ignored. This is what the result looks like in the console. Home Work Predicates also work great with relationships.

Replace the previous example with the following: In the example, we instantiate two predicates and turn them into a compound predicate, using the NSCompoundPredicate class. The first predicate restricts the fetch request to item records that are marked as completed.

core data predicate relationship swift

The second predicate specifies that we are only interested in item records that belong to a list record that has a name equal to Home. Run the application and inspect the result in the console.

Now that you know what Core Data is and how the Core Data stack is set up, it's time to write some code.