使用mongoose将值作为参数发送到mongodb中以检查是否存在

mongoose.connect('mongodb://localhost/mydatabase', { useNewUrlParser: true, useUnifiedTopology: true })
  .then(() => {
    console.log('Connected to MongoDB');
  })
  .catch((error) => {
    console.error('Error connecting to MongoDB:', error);
  });

const userSchema = new mongoose.Schema({
  username: String
});

const User = mongoose.model('User', userSchema);

User.findOne({ username: 'testUser' })
  .then((user) => {
    if (user) {
      console.log('User exists');
    } else {
      console.log('User does not exist');
    }
  })
  .catch((error) => {
    console.error('Error querying user:', error);
  });