DPS923 MAP523 Week 9 Notes
Thursday, March 5 - classroom lecture
Monday, March 9 - hands-on in the computer-lab
More work with Core Data this week and next.
Thursday, March 5
We will cover these - discuss, show-and-tell, diagram, etc. - in the Thursday class. While some brief notes are included below, be prepared to take your own notes.
A version 2 of the project template.
Fetch request essentials.
Fetched results controller essentials.
Syntax comparisons among data store technologies.
Core Data essentials summary.
A reminder to learn via the code examples.
Monday, March 9
Your goal today is to create an app that uses a Core Data store. It will display data based on something that Mockaroo can easily generate. Here’s what to do:
TemplateCDv2 to create an app. Do the “rename” tasks to a project name that makes sense.
Visit mockaroo.com. Generate 150 rows of JSON data. Configure the fields so that you have at least one field that gets values that repeat somewhat (e.g. states, provinces, car makes, etc. - look around; don’t be lazy).
Add that JSON file to your project.
Use the code example to learn how to load the JSON data into a Core Data store.
Change the “list” table view controller to display the data.
In #5 above, we suggest that you use a simpler fetch request object first, to fetch the data.
Then, adapt the code, changing it to use a fetched results controller object. Obviously, the cell rendering code will have to change a bit.
The course’s GitHub repo has code examples for many topics and techniques. You can download a zip of the code repo, or clone it.
- W09a1LoadV1 (programmatic load of some objects)
- W09a2LoadV2 (load from a JSON file in the app bundle)
- TemplateCDv2 (in the templates and solutions folder)
Here’s a list of topics that we learned something about this week:
- A fetch request is an important object in a Core Data app, as you learned last week.
- It can be used to fetch all, some (filtered), one (to match a value), and then optionally ordered or sequenced in some way.
- A fetch request will return a typed array of results. It will typically never have an error, but it’s possible that the result array will be empty.
- Each generated entity class has a
fetchRequest() method that will create a fetch request object.
- To execute/run the request, use the context’s
fetch() method, and assign the results to a variable.
- A predicate is an object (in Swift) that enables a developer to filter or constrain the selection, if desired.
- A predicate has two important parts, that can be thought of as a conditional statement that you would have anywhere (as in an
if statment). The first part is the predicate string, and the other is the argument(s).
- A predicate can be simple, with known and statically-coded string (to identify the filtered property) and argument. For example, “age < 25”.
- It can also be coded to accept an argument (e.g. “age < %@”).
- A predicate can also be dynamic with regards to filter property, and it can be complex by having multiple filter conditions.
NSPredicate class is used to create a predicate.
- A sort descriptor is an object (in Swift) that enables a developer to order or sequence the selection, if desired.
- A fetch request has an array of zero or more sort descriptors. Yes, it’s possible to sort results by “age”, then by “last name”, and finally by “first name”.
- A sort descriptor has a
key to identify the property to sort on, and a boolean value to declare whether the results are in
- You should be able to code, almost from memory, the typical create-and-use tasks for a fetch request.
- In some scenarios (what are they?), it is more useful to use a fetched results controller (frc).
- Inside a frc, there is a familiar fetch request object.
- An frc has a convenience method to perform the fetch. The returned results are still a typed array, and put in a
- The frc is purpose-built to work with a table view controller, as its data source, and listener for events that arise through user interaction.
- You should be able to code, almost from memory, the typical create-and-use tasks for an frc.
- You should be able to learn at least five new coding tasks and strategies by studying the code examples.