Mongoose is a JavaScript library that provides methods to interact with a MongoDB database. Mongoose translates JavaScript objects (JSON) to BSON data in a MongoDB database, and vice versa.

Mongoose interactions are based on Schema and Model declarations.

• A Schema defines the shape of the documents within that collection.
• A Model maps to a MongoDB collection and its documents.

Mongoose Schema

Remember, each record in a MongoDB database is a document with key/value pairs as entries. Using Mongoose’s Schema, we can set the structure of those documents dynamically.

Imagine you were creating a Schema for the database of a web-based poetry application where you could both write and publish poems. Each key in our poemSchema will define a property in our documents which will be cast to its associated SchemaType.

const poemSchema = new mongoose.Schema({
  title: String
})

Each document that is derived from the poemSchema above will have a title property with a string saved to it.

Mongoose will cast mismatched data types to the specified SchemaType. For example, if we entered the number 1 as a title for a poem, Mongoose would cast the entry so that it entered that database as a string "1". Using casting, Mongoose ensures that string properties are assigned strings values.