TypeORM By Example: Part 5

Exploring one-to-one relationships.

This article is part of a series starting with TypeORM By Example: Part 1.

The final example for this article is available for download.

Having spent so much time on other TypeORM topics, we finally get to the obvious topic of relationships; one-to-one, one-to-many, and many-to-many.

One-to-One Relationship — Defining

Let us implement a TodoMetadata entity to hold a single comment about a Todo.

src / entity / TodoMetadata

and update Todo to hold a reference to a TodoMetadata.

src / entity / Todo.ts

We build the application and generate a migration:

npm run build-ts
./node_modules/.bin/typeorm migration:generate -n TodoMetadata

the migration:

src / migration / 1535970439120-TodoMetadata.ts

We build the application and run the migration:

npm run build-ts
npm run start

The migration runs and we see our new todo_metadata table.

One-to-One Relationship — Creating

Let us now update the application to create the TodoMetadata alongside the Todo.

src / todoManager.ts

Observations:

• We rename the Todo repository and create a basic one for TodoMetadata
• We create a TodoMetadata and assign it to a Todo
• We need to save the TodoMetadata first; so that its id is assigned. After it is saved, we can save the Todo.

Looking at the log, we can see the updated code in action; first saving the TodoMetadata and the the Todo.

One-to-One Relationship — Reading

We update the TodoRepository with the relations in both the find and QueryBuilder syntax:

src / TodoRepository.ts

note: On a first pass at this, I named the Todo field todoMetadata instead of metadata. Ran into all sorts of trouble trying to get the QueryBuilder to work with this camel-case name.

Now with this in place, our queries return the todos with the metadata.

Next Steps

In the next article, TypeORM By Example: Part 6 we continue our exploration of one-to-many relationships.

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