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Update Android relationship docs to account for cascading delete #109

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Update Android relationship docs to account for cascading delete #109

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1afad90
Update java_relationship to account for cascading delete
richardmcclellan Feb 4, 2021
b027568
Update markdown/tests/android/java_relationship.md
richardmcclellan Feb 4, 2021
0c5b211
Update markdown/tests/android/kotlin_relationship.md
richardmcclellan Feb 4, 2021
769838c
Update markdown/tests/android/kotlin_relationship.md
richardmcclellan Feb 4, 2021
ab4d21f
Fix indentation
richardmcclellan Feb 4, 2021
98ed0f4
Simply success log message for deleting target model
richardmcclellan Feb 5, 2021
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178 changes: 89 additions & 89 deletions markdown/tests/android/java_relationship.md
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Original file line number Diff line number Diff line change
Expand Up @@ -9,21 +9,21 @@ In order to save a 1:1 relationship, create the target model instance first and

```java
Author newAuthor = Author.builder()
.name("Rene Brandel")
.build();
.name("Rene Brandel")
.build();
Post post = Post.builder()
.content("My first post!")
.author(newAuthor)
.build();
.content("My first post!")
.author(newAuthor)
.build();

Amplify.DataStore.save(newAuthor,
savedAuthor -> {
Amplify.DataStore.save(post,
savedPost -> Log.i("Amplify DataStore", "Post saved."),
failure -> Log.e("Amplify DataStore", "Error while saving:", failure)
);
},
failure -> Log.e("Amplify DataStore", "Error while saving:", failure)
savedAuthor -> {
Amplify.DataStore.save(post,
savedPost -> Log.i("Amplify DataStore", "Post saved."),
failure -> Log.e("Amplify DataStore", "Error while saving:", failure)
);
},
failure -> Log.e("Amplify DataStore", "Error while saving:", failure)
);
```
Here we've first created a new `Author` instance and then saved it to the `Post`'s "author" relationship field.
Expand All @@ -34,13 +34,13 @@ To query one-to-one relationships, access the target model instance through its

```java
Amplify.DataStore.query(Post.class,
matches -> {
while (matches.hasNext()) {
Post post = matches.next();
Author author = post.getAuthor();
}
},
failure -> Log.e("Amplify DataStore", "Query failed.", failure)
matches -> {
while (matches.hasNext()) {
Post post = matches.next();
Author author = post.getAuthor();
}
},
failure -> Log.e("Amplify DataStore", "Query failed.", failure)
);
```

Expand All @@ -50,12 +50,22 @@ In one-to-one relationships, if the target model instance is deleted, it will al

```java
Amplify.DataStore.delete(author,
deleted -> Log.i("Amplify DataStore", "Author + Post deleted"),
failure -> Log.e("Amplify DataStore", "Deletion failed", failure));
deleted -> Log.i("Amplify DataStore", "Author deleted."),
failure -> Log.e("Amplify DataStore", "Deletion failed", failure));
```

In this example, the `Post`'s "author" field will be cleared and the `Author` model instance will be deleted.

If the source model is deleted, the target model will be automatically deleted as well.

```java
Amplify.DataStore.delete(post,
deleted -> Log.i("Amplify DataStore", "Author + Post deleted"),
failure -> Log.e("Amplify DataStore", "Deletion failed", failure));
```

In this example, the `Post` model instance will be deleted and the `Author` model instance will be deleted, locally, and on the backend.

@raphkim raphkim Feb 4, 2021

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Doesn't Author have one-to-many relationship with Post? That means deleting post will not affect authors. Only if Author gets deleted, then will Post belonging to that specific Author will get deleted.

@raphkim raphkim Feb 4, 2021

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Ooooh, I just looked at the original doc, and I think the document is wrong?

Example: One post (source model) has one author (target model).

Document describes that Post has-one Author, but the models are the other way around... This should probably be fixed.

@richardmcclellan richardmcclellan Feb 4, 2021

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Doesn't Author have one-to-many relationship with Post?

I agree, realistically this would probably be a one-to-many, because an Author would never be restricted to just one Post. I'm actually struggling to think of a good use case for @HasOne at all. I think for now, we can stick with this example.

Document describes that Post has-one Author, but the models are the other way around... This should probably be fixed.

The question is - when deleting a Post, should it delete the Author? (this is how the document reads now) Or when deleting an Author, should it delete the Post (this is what you are proposing). I think either is valid, it just depends on the use case.

@raphkim raphkim Feb 9, 2021

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Since Post has one Author, your edit is correct! :)

My only concern at the moment is that the other parts of the document (not edited in this PR) is currently incorrect.


:::NEW_COMMAND:::
:::ONE_TO_MANY:::

Expand All @@ -67,22 +77,22 @@ In order to save a one-to-many relationship, create the source model instance fi

```java
Publication publication = Publication.builder()
.title("Amplify Weekly")
.build();
.title("Amplify Weekly")
.build();

Article article = Article.builder()
.publicationId(publication.getId())
.title("Add auth to your app in 3 steps")
.build();
.publicationId(publication.getId())
.title("Add auth to your app in 3 steps")
.build();

Amplify.DataStore.save(publication,
savedPublication -> {
Amplify.DataStore.save(article,
savedArticle -> Log.i("Amplify DataStore", "Article saved." + savedArticle),
failure -> Log.e("Amplify DataStore", "Error while saving:", failure)
);
},
failure -> Log.e("Amplify DataStore", "Error while saving:", failure)
savedPublication -> {
Amplify.DataStore.save(article,
savedArticle -> Log.i("Amplify DataStore", "Article saved." + savedArticle),
failure -> Log.e("Amplify DataStore", "Error while saving:", failure)
);
},
failure -> Log.e("Amplify DataStore", "Error while saving:", failure)
);
```
Here we've first created a new `Publication` instance and then saved its _id_ to the `Article`'s "publicationID" relationship field.
Expand All @@ -93,40 +103,30 @@ To query one-to-many relationships, filter based on the source model instance's

```java
Amplify.DataStore.query(Article.class, Where.matches(Article.PUBLICATION_ID.eq("YOUR_PUBLICATION_ID")),
matches -> {
while(matches.hasNext()) {
Article article = matches.next();
Log.i("Amplify DataStore", "Matched article: " + article);
}
},
failure -> Log.e("Amplify DataStore", "Query failed.", failure));
matches -> {
while(matches.hasNext()) {
Article article = matches.next();
Log.i("Amplify DataStore", "Matched article: " + article);
}
},
failure -> Log.e("Amplify DataStore", "Query failed.", failure));
```

**Delete**

In one-to-many relationships, delete the target model instance first and then delete the source model.
In one-to-many relationships, deleting the source model will automatically delete all target models that belong to it, both locally, and on the backend.

@raphkim raphkim Feb 4, 2021

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I personally prefer "parent and child" over "source and target" because I think it's clearer, but I can see the value in keeping a consistent language across different platforms too. What do you think?

@richardmcclellan richardmcclellan Feb 4, 2021

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I like "parent and child" better as well, but consistency across platforms is most important. @renebrandel what do you think about changing this wording across all platforms to "parent and child" instead of "source and target"?


```java
Amplify.DataStore.query(Article.class, Where.matches(Article.PUBLICATION_ID.eq("YOUR_PUBLICATION_ID")),
matches -> {
while (matches.hasNext()) {
Article article = matches.next();
Amplify.DataStore.delete(article,
deletedArticle -> Log.i("Amplify DataStore", "Article deleted"),
failure -> {});
}
Amplify.DataStore.query(Publication.class, Where.id("YOUR_PUBLICATION_ID"),
matchedPublications -> {
while(matchedPublications.hasNext()) {
Publication match = matchedPublications.next();
Amplify.DataStore.delete(match,
deleted -> Log.i("Amplify DataStore", "Publication deleted"),
failure -> Log.e("Amplify DataStore", "Deletion failed.", failure));
}
},
failure -> {});

}, failure -> {}
Amplify.DataStore.query(Publication.class, Where.id("YOUR_PUBLICATION_ID"),

@raphkim raphkim Feb 4, 2021

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Just something to note: we don't yet have the fix for ambiguity introduced by Where.id() method...

@richardmcclellan richardmcclellan Feb 4, 2021 •
edited
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Hmm, wasn't it fixed by aws-amplify/amplify-android#1133 to default to the class being queried? In this case, Publication, so this should actually work?

@raphkim raphkim Feb 4, 2021

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No adjustment was made to Where.id() yet. I haven't yet found a clean way to implement it.

matchedPublications -> {
while (matchedPublications.hasNext()) {
Publication match = matchedPublications.next();
Amplify.DataStore.delete(match,
deleted -> Log.i("Amplify DataStore", "Publication and all related Article instances deleted"),
failure -> Log.e("Amplify DataStore", "Deletion failed.", failure));
}
},
failure -> {}
);
```

Expand All @@ -145,30 +145,30 @@ In order to save a many-to-many relationship, create both model instance first a

```java
Post post = Post.builder()
.body("How to build deploy a web app on AWS Amplify")
.build();
.body("How to build deploy a web app on AWS Amplify")
.build();

Tag tag = Tag.builder()
.label("static-web-hosting")
.build();
.label("static-web-hosting")
.build();

PostTag postTag = PostTag.builder()
.post(post)
.tag(tag)
.build();
.post(post)
.tag(tag)
.build();

Amplify.DataStore.save(post,
savedPost -> {
Log.i("Amplify DataStore", "post saved.");
Amplify.DataStore.save(tag,
savedEditor -> {
Log.i("Amplify DataStore", "Tag saved.");
Amplify.DataStore.save(postTag,
saved -> Log.i("Amplify DataStore", "PostTag saved."),
failure -> Log.e("Amplify DataStore", "PostTag not saved.", failure)
);
},
failure -> Log.e("Amplify DataStore", "Tag not saved.", failure)
savedEditor -> {
Log.i("Amplify DataStore", "Tag saved.");
Amplify.DataStore.save(postTag,
saved -> Log.i("Amplify DataStore", "PostTag saved."),
failure -> Log.e("Amplify DataStore", "PostTag not saved.", failure)
);
},
failure -> Log.e("Amplify DataStore", "Tag not saved.", failure)
);
},
failure -> Log.e("Amplify DataStore", "Post not saved.", failure)
Expand All @@ -183,12 +183,12 @@ To query many-to-many relationships, filter the join model based on one of the m

```java
Amplify.DataStore.query(ContentTag.class, Where.matches(ContentTag.CONTENT.eq("YOUR_CONTENT_ID")),
matches -> {
while (matches.hasNext()) {
ContentTag contentTag = matches.next();
Log.i("Amplify DataStore", "Tag: " + contentTag.getTag());
}
}, failure -> {});
matches -> {
while (matches.hasNext()) {
ContentTag contentTag = matches.next();
Log.i("Amplify DataStore", "Tag: " + contentTag.getTag());
}
}, failure -> {});
```

In this example, first filter the _join model_ `PostTag` with your `Post`'s _id, then map the `PostTag`s to `Tag`s.
Expand All @@ -199,18 +199,18 @@ Deleting the _join model instance_ will not delete any source model instances.

```java
Amplify.DataStore.delete(
toBeDeletedPostTag,
deleted -> Log.i("Amplify DataStore", "Deleted " + deleted),
failure -> Log.e("Amplify DataStore", "Deletion failed", failure));
toBeDeletedPostTag,
deleted -> Log.i("Amplify DataStore", "Deleted " + deleted),
failure -> Log.e("Amplify DataStore", "Deletion failed", failure));
```
Both the `Post` and the `Tag` instances will not be deleted. Only the join model instances containing the link between a `Post` and a `Tag`.

Deleting a _source model instance_ will also delete the join model instances containing the source model instance.
```java
Amplify.DataStore.delete(
toBeDeletedTag,
deleted -> Log.i("Amplify DataStore", "Deleted " + deleted),
failure -> Log.e("Amplify DataStore", "Deletion failed", failure));
toBeDeletedTag,
deleted -> Log.i("Amplify DataStore", "Deleted " + deleted),
failure -> Log.e("Amplify DataStore", "Deletion failed", failure));

```
The `toBeDeletedTag` `Tag` instance and all `PostTag` instances where _tag_ is linked to `toBeDeletedTag` will be deleted.
The `toBeDeletedTag` `Tag` instance and all `PostTag` instances where _tag_ is linked to `toBeDeletedTag` will be deleted.
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