mongodb中如何限制父节点的最大引用

使用MongoDB限制父节点的最大引用

javascript
const mongoose = require('mongoose');
// 定义父节点模型
const parentSchema = new mongoose.Schema({
  name: String,
  children: [{
    type: mongoose.Schema.Types.ObjectId,
    ref: 'Child'
  }]
});
// 定义子节点模型
const childSchema = new mongoose.Schema({
  name: String
});
// 在保存和更新操作前检查引用数量
parentSchema.pre('save', function(next) {
  if (this.children.length > 3) {
    const error = new Error('引用数量超过限制');
    return next(error);
  }
  next();
});
// 创建模型
const Parent = mongoose.model('Parent', parentSchema);
const Child = mongoose.model('Child', childSchema);
// 测试代码
(async () => {
  try {
    await mongoose.connect('mongodb://localhost/test', {
      useNewUrlParser: true,
      useUnifiedTopology: true
    });
    // 创建父节点
    const parent = new Parent({ name: '父节点' });
    // 创建子节点
    const child1 = new Child({ name: '子节点1' });
    const child2 = new Child({ name: '子节点2' });
    const child3 = new Child({ name: '子节点3' });
    const child4 = new Child({ name: '子节点4' });
    // 将子节点添加到父节点
    parent.children.push(child1);
    parent.children.push(child2);
    parent.children.push(child3);
    parent.children.push(child4); // 超过限制，会触发错误
    // 保存父节点
    await parent.save();
    console.log('保存成功');
  } catch (error) {
    console.error('保存失败:', error.message);
  } finally {
    mongoose.disconnect();
  }
})();