如何使用Mongoose和node连接到特定的数据库？

npm install mongoose

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost:27017/mydatabase', { useNewUrlParser: true, useUnifiedTopology: true });

const db = mongoose.connection;
db.once('open', () => {
  console.log('Connected to the database');
});
db.on('error', (error) => {
  console.error('Error connecting to the database:', error);
});

const userSchema = new mongoose.Schema({
  username: String,
  email: String
});
const User = mongoose.model('User', userSchema);

const newUser = new User({ username: 'John', email: 'john@example.com' });
newUser.save((error, savedUser) => {
  if (error) {
    console.error('Error creating user:', error);
  } else {
    console.log('User created:', savedUser);
  }
});

User.find({}, (error, users) => {
  if (error) {
    console.error('Error querying users:', error);
  } else {
    console.log('Users:', users);
  }
});

User.updateOne({ username: 'John' }, { email: 'newemail@example.com' }, (error, result) => {
  if (error) {
    console.error('Error updating user:', error);
  } else {
    console.log('User updated:', result);
  }
});

User.deleteOne({ username: 'John' }, (error) => {
  if (error) {
    console.error('Error deleting user:', error);
  } else {
    console.log('User deleted');
  }
});