Mongoose populate

While working on a MERN stack project, I came across a situation where I wanted to populate a field but also populate a field inside mongoose populate populated field I know it's confusing, mongoose populate. Bear with me :p.

Mongoose has a more powerful alternative called populate , which lets you reference documents in other collections. Population is the process of automatically replacing the specified paths in the document with document s from other collection s. We may populate a single document, multiple documents, plain object, multiple plain objects, or all objects returned from a query. Let's look at some examples. So far we've created two Models. Our Person model has its stories field set to an array of ObjectId s. The ref option is what tells Mongoose which model to use during population, in our case the Story model.

Mongoose populate

Mongoose has a more powerful alternative called populate , which lets you reference documents in other collections. Population is the process of automatically replacing the specified paths in the document with document s from other collection s. We may populate a single document, multiple documents, a plain object, multiple plain objects, or all objects returned from a query. Let's look at some examples. So far we've created two Models. Our Person model has its stories field set to an array of ObjectId s. The ref option is what tells Mongoose which model to use during population, in our case the Story model. However, you should use ObjectId unless you are an advanced user and have a good reason for doing so. So far we haven't done anything much different. We've merely created a Person and a Story. Now let's take a look at populating our story's author using the query builder:.

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There are no joins in MongoDB but sometimes we still want references to documents in other collections. This is where population comes in. Population is the process of automatically replacing the specified paths in the document with document s from other collection s. We may populate a single document, multiple documents, plain object, multiple plain objects, or all objects returned from a query. Let's look at some examples. So far we've created two Models.

Query constructor used for building queries. You do not need to instantiate a Query directly. Instead use Model functions like Model. Be sure to read about all of its caveats before using. Setting this option is a no-op for MongoDB 4. Calling query. Executes the query returning a Promise which will be resolved with either the doc s or rejected with the error.

Mongoose populate

In Mongoose, populate lets you pull in referenced documents from another collection. Populate is similar to a left outer join in SQL , but the difference is that populate happens in your Node. Mongoose executes a separate query under the hood to load the referenced documents. Suppose you have two Mongoose models : Movie and Person. Movie documents have a director and an array of actors. Mongoose queries have a populate function that lets you load a movie and its corresponding director and actors in one line:.

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The Principle of Least Cardinality states that one-to-many relationships, like author to blog post, should be stored on the "many" side. Bear with me :p. You can manually populate a property by setting it to a document. Output after using the populate method in the code. View full discussion 54 comments. Take caution when calling its remove method because you'll be removing it from the database, not just the array. So far we've created two Models. You have to try it once to see the outcome. Contribute to the GeeksforGeeks community and help create better learning resources for all. Once unsuspended, paras will be able to comment and publish posts again. Populate is good for simple to intermediate scenarios but aggregation is more helpful when you need to handle a little complex to advance scenarios. For example, suppose you have 2 stories:. Some points about populate: If no document is found to populate, then field will be null. However, that's sometimes not the right choice. Dec 28,

Mongoose has a more powerful alternative called populate , which lets you reference documents in other collections.

There are two perspectives to this story. Instead we could skip populating and directly find the stories we are interested in. There are no joins in MongoDB but sometimes we still want references to documents in other collections. If you have an array of authors in your storySchema , populate will give you an empty array instead. But I don't know about pre query middlewares. Here is what you can do to flag paras Make all posts by paras less visible paras consistently posts content that violates DEV Community's code of conduct because it is harassing, offensive or spammy. Unfortunately, these two schemas, as written, don't support populating an author's list of blog posts. Please Login to comment I came across it when I was thinking the same thing. In the above example, events and conversations are stored in separate MongoDB databases. Mongoose QueriesModel. Now that we've covered populate , let's take a look at discriminators. There are two perspectives here. Programmer since age 12, always exploring new tech and fields with a thirst for knowledge.