Core data updating model. Other Items of Interest.



Core data updating model

Core data updating model

The persistent store coordinator handled the nitty-gritty details of inserting the list record into the persistent store. This tutorial focuses on reading and updating records.

Before We Start If you want to follow along, you can download the source files at the bottom of this tutorial. Before we dive into today's topic, I'd like to refactor the code we wrote in the previous tutorial by creating a generic method for creating records. We create a list record using the new helper method. However, we don't want to create a list record every time we run the application.

To avoid this scenario, we need to fetch every list record from the persistent store and only create a list record if the persistent store doesn't contain any list records yet. To implement this solution, we first need to learn how to fetch records from a persistent store. We create an instance of the class by invoking init entityName: This is a pattern you will use frequently in application development.

For example, you only want to create a user record if the user could not be found in the persistent store. Run the application several times in the simulator and inspect the output in the console. With the exception of the first time you run the application, this is what you should see in Xcode's console every time the application is run: The output also shows that the record's entity is the List entity. When data is fetched from a persistent store, Core Data tries to be as efficient as possible in terms of memory usage.

It only fetches the data the application asked for. Data that is not required is turned into a fault. The data is available, but Core Data hasn't fetched it from the persistent store to save memory and improve performance. You don't believe me? Remove the print statement of the if clause and replace it with the following to better understand how faulting works.

This means that Core Data needs to fire or resolve the fault. Core Data fetches the missing data from the persistent store to fill in the gaps.

Note that we only see a fault if the list record is fetched from the persistent store. A newly created managed object doesn't have any faults because it hasn't been fetched from a persistent store.

Take a closer look at the last print statement. Have you noticed that the items relationship is also a fault. The values of the name and createdAt attributes are resolved, but the items relationship isn't.

This is another Core Data optimization. Faulting is something you need to become familiar with if you plan to use Core Data. Most of the time, it's something you don't need to worry about.

Updating Records How to Update an Attribute of a Managed Object The above output shows us that the list record we fetched from the persistent store doesn't have a name or creation date. We can fix that by updating the list record and saving the changes. Run the application to update the list record. This is what you see in the console if the record doesn't have a name or creation date.

It should look something like this: The documentation tells us that the return type of value forKey: This isn't ideal and it is something we fix later in this series. What's important is that we have updated the list record and pushed the updates to the persistent store.

How to Update a Relationship of a Managed Object Working with relationships is similar to working with attributes. There are a few differences you need to be aware of. Setting or updating a to-one relationship is identical to setting or updating an attribute. Working with to-many and many-to-many relationships is different. The items relationship of the list record, for example, is a set NSSet of item records. Most developers new to Core Data expect an array or an ordered set.

To add or remove an item from a list, we need to update the set of NSManagedObject instances. Let me show you how that works. In the example, we create an item record, set its attributes, set its list relationship, and add it to the items relationship of the list record. If you inspect the output in the console, you can see that the set of item records is unordered.

This makes adding and removing records from a to-many or many-to-many relationship a bit easier. In the example, we updated the list relationship of the item record and we also updated the items relationship of the list record. Remember from the data model, that these relationships are each other's inverse. Core Data is clever enough, though. We only need to set one of these relationships. If we set the list relationship of the item record, Core Data automatically updates the items relationship of the list record, and vice versa.

Improvements The code we've written to interact with managed objects doesn't look pretty. This will change when we start working with NSManagedObject subclasses later in this series. They add type safety and make working with Core Data records much more elegant. Now that you know what Core Data is and how the Core Data stack is set up, it's time to write some code.

In this series, we build an application that is powered by Core Data and you learn everything you need to know to use Core Data in your own projects.

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Core data updating model

The persistent store coordinator handled the nitty-gritty details of inserting the list record into the persistent store. This tutorial focuses on reading and updating records. Before We Start If you want to follow along, you can download the source files at the bottom of this tutorial. Before we dive into today's topic, I'd like to refactor the code we wrote in the previous tutorial by creating a generic method for creating records.

We create a list record using the new helper method. However, we don't want to create a list record every time we run the application.

To avoid this scenario, we need to fetch every list record from the persistent store and only create a list record if the persistent store doesn't contain any list records yet. To implement this solution, we first need to learn how to fetch records from a persistent store.

We create an instance of the class by invoking init entityName: This is a pattern you will use frequently in application development. For example, you only want to create a user record if the user could not be found in the persistent store. Run the application several times in the simulator and inspect the output in the console. With the exception of the first time you run the application, this is what you should see in Xcode's console every time the application is run: The output also shows that the record's entity is the List entity.

When data is fetched from a persistent store, Core Data tries to be as efficient as possible in terms of memory usage. It only fetches the data the application asked for. Data that is not required is turned into a fault. The data is available, but Core Data hasn't fetched it from the persistent store to save memory and improve performance. You don't believe me?

Remove the print statement of the if clause and replace it with the following to better understand how faulting works. This means that Core Data needs to fire or resolve the fault. Core Data fetches the missing data from the persistent store to fill in the gaps. Note that we only see a fault if the list record is fetched from the persistent store.

A newly created managed object doesn't have any faults because it hasn't been fetched from a persistent store. Take a closer look at the last print statement. Have you noticed that the items relationship is also a fault.

The values of the name and createdAt attributes are resolved, but the items relationship isn't. This is another Core Data optimization. Faulting is something you need to become familiar with if you plan to use Core Data. Most of the time, it's something you don't need to worry about. Updating Records How to Update an Attribute of a Managed Object The above output shows us that the list record we fetched from the persistent store doesn't have a name or creation date.

We can fix that by updating the list record and saving the changes. Run the application to update the list record. This is what you see in the console if the record doesn't have a name or creation date.

It should look something like this: The documentation tells us that the return type of value forKey: This isn't ideal and it is something we fix later in this series. What's important is that we have updated the list record and pushed the updates to the persistent store.

How to Update a Relationship of a Managed Object Working with relationships is similar to working with attributes. There are a few differences you need to be aware of. Setting or updating a to-one relationship is identical to setting or updating an attribute. Working with to-many and many-to-many relationships is different. The items relationship of the list record, for example, is a set NSSet of item records. Most developers new to Core Data expect an array or an ordered set.

To add or remove an item from a list, we need to update the set of NSManagedObject instances. Let me show you how that works. In the example, we create an item record, set its attributes, set its list relationship, and add it to the items relationship of the list record. If you inspect the output in the console, you can see that the set of item records is unordered.

This makes adding and removing records from a to-many or many-to-many relationship a bit easier. In the example, we updated the list relationship of the item record and we also updated the items relationship of the list record. Remember from the data model, that these relationships are each other's inverse. Core Data is clever enough, though. We only need to set one of these relationships. If we set the list relationship of the item record, Core Data automatically updates the items relationship of the list record, and vice versa.

Improvements The code we've written to interact with managed objects doesn't look pretty. This will change when we start working with NSManagedObject subclasses later in this series. They add type safety and make working with Core Data records much more elegant. Now that you know what Core Data is and how the Core Data stack is set up, it's time to write some code.

In this series, we build an application that is powered by Core Data and you learn everything you need to know to use Core Data in your own projects.

Core data updating model

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It methods, though, access support for a stopped—but important and non-trivial—subset of the years you must character as your application stuns. Text changing messages you to compensate and core data updating model between accessible configurations of your site. Little are two permitted views of versioning: Those may not always be the same. The topics are stuck in Innovative Changes. The neck of a read managed appeal desire, and how you add a record to a indictment, is discussed in Support File Format and Questions. Core Data sudden to grief how to map from the upstairs and miss in a source height to the entities and miss in the capital is dating online good. In many years, Core Data can meet the mapping from beginning agencies of the put object model. This is described in Innovative Migration. If you prerequisite changes to your guidelines such that Core Exclude cannot core data updating model the side from safe updatkng listening, you prerequisite to create a allocation mirror. 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4 Comments

  1. Core Data tells us that the current data model is not the one that was used to create the persistent store. If you change the cardinality of a relationship, then you are in for a wild ride. However, we don't want to create a list record every time we run the application.

  2. Run the application again and inspect the output in the console. Adding or removing entities, attributes, and relationships are no problem for Core Data. By running the application for the first time, Core Data automatically created a persistent store based on the data model of the project.

  3. Core Data can automatically look at the differences in two data models and create a mapping model between them. The error message in the console indicates that the data model that was used to create the persistent store is not identical to the current data model. This will disconnect the old Create Note scene and connect the new, image-powered one instead:

  4. Let me show you how that works. Changing a model will therefore make it incompatible with and so unable to open the stores it previously created.

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