How do you define a schema in Mongoose?

Mongoose is an Object Data Modeling (ODM) library for MongoDB and Node.js. It provides a schema-based solution to model application data, simplifying database interactions by providing a more structured way to define data models and validating data before it is saved to the database. 
 
Explain Mongoose's role in a Node.js application.

In Mongoose, you define a schema using the `mongoose.Schema` class. For example, to create a user schema, you might write: `const userSchema = new mongoose.Schema({ name: String, age: Number });`. This structure allows you to enforce data types and validation rules. 
 
Create a simple user schema.

Models in Mongoose are constructors compiled from schemas. They allow you to create and manage documents within a collection. For instance, after defining a schema, you can create a model with `const User = mongoose.model('User', userSchema);`, enabling operations like `User.find()`. 
 
Create a model from a schema.

To connect to a MongoDB database using Mongoose, you use the `mongoose.connect()` method. For example: `mongoose.connect('mongodb://localhost:27017/mydatabase', { useNewUrlParser: true, useUnifiedTopology: true });`. This establishes a connection to the specified database with options for parsing and topology. 
 
Show how to connect to MongoDB.

Mongoose middlewares are functions that are executed at certain stages of a document's lifecycle. For example, you can define a pre-save hook: `userSchema.pre('save', function(next) { this.age = Math.abs(this.age); next(); });`. This executes before saving, allowing you to modify data. 
 
Explain pre and post hooks.