Really not feeling it today. Like at all.
Went through another section of Mongo training. This one actually talked about a pretty interesting topic of how to handle relationships within mongodb. So this means being able to related documents within different collections to one another. I honestly didn’t even know that was a thing.
Today’s going to be another note dump day. Forgive me:
Referencing between collections
- Setting up references between documents between collections (think relational DB)
- Assign an object with type
Schema.Types.ObjectId and a ref equal to a model name:
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const BlogPostSchema = new Schema({
title: String,
content: String,
comments: [{
type: Schema.Types.ObjectId,
ref: 'comment'
}]
});
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- This ref value MUST match what’s being defined in model, as shown below:
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const Comment = mongoose.model('comment', CommentSchema);
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- Mongoose does magic behind the scenes when associating the data. In the following steps, Mongoose is actually handling the id referencing:
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joe = new User({name: 'Joe'});
blogPost = new BlogPost({
title: 'JS is great',
content: 'Sure it is'
});
comment = new Comment({
content: 'This is a comment'
});
joe.blogPosts.push(blogPost);
blogPost.comments.push(comment);
comment.user = joe;
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- When doing a query, you can add on a
populate modifier to fill in the data for a specific field:
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it.only('saves a relation between a user and a blog post', (done) => {
User.findOne({ name: 'Joe' })
.populate('blogPosts')
.then((user) => {
console.log(user);
done();
});
});
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- There is no way to recursively crawl like this. You only get one.
- Mongoose will not allow it
- … But evidently there is a way to do it? Not sure why it was said that it wasn’t possible:
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it.only('saves a full relation tree', (done) => {
User.findOne({name:'Joe'})
.populate({
path: 'blogPosts',
populate: {
path: 'comments',
model: 'comment',
populate: {
path: 'user',
model: 'user'
}
}
})
.then((user) => {
assert(user.name === 'Joe');
assert(user.blogPosts[0].title === 'JS is great');
assert(user.blogPosts[0].comments[0].content === 'This is a comment');
assert(user.blogPosts[0].comments[0].user.name === 'Joe');
done();
});
});
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💚