查询转换

Model.find()，Query#find()，Model.findOne() 等方法的第一个参数称为 filter。 在旧内容中，此参数有时被称为 query 或 conditions。 例如

const query = Character.find({ name: 'Jean-Luc Picard' });
query.getFilter(); // `{ name: 'Jean-Luc Picard' }`

// Subsequent chained calls merge new properties into the filter
query.find({ age: { $gt: 50 } });
query.getFilter(); // `{ name: 'Jean-Luc Picard', age: { $gt: 50 } }`

当您使用 Query#exec() 或 Query#then() 执行查询时，Mongoose 会将过滤器转换以匹配您的模式。

// Note that `_id` and `age` are strings. Mongoose will cast `_id` to
// a MongoDB ObjectId and `age.$gt` to a number.
const query = Character.findOne({
  _id: '5cdc267dd56b5662b7b7cc0c',
  age: { $gt: '50' }
});

// `{ _id: '5cdc267dd56b5662b7b7cc0c', age: { $gt: '50' } }`
// Query hasn't been executed yet, so Mongoose hasn't casted the filter.
query.getFilter();

const doc = await query.exec();
doc.name; // "Jean-Luc Picard"

// Mongoose casted the filter, so `_id` became an ObjectId and `age.$gt`
// became a number.
query.getFilter()._id instanceof mongoose.Types.ObjectId; // true
typeof query.getFilter().age.$gt === 'number'; // true

如果 Mongoose 无法将过滤器转换为您的模式，您的查询将抛出 CastError 错误。

const query = Character.findOne({ age: { $lt: 'not a number' } });

const err = await query.exec().then(() => null, err => err);
err instanceof mongoose.CastError; // true
// Cast to number failed for value "not a number" at path "age" for
// model "Character"
err.message;

strictQuery 选项

默认情况下，Mongoose 不会 转换模式中不存在的过滤器属性。

const query = Character.findOne({ notInSchema: { $lt: 'not a number' } });

// No error because `notInSchema` is not defined in the schema
await query.exec();

您可以使用模式的 strictQuery 选项 来配置此行为。此选项类似于 strict 选项。将 strictQuery 设置为 true 会从过滤器中删除非模式属性。

mongoose.deleteModel('Character');
const schema = new mongoose.Schema({ name: String, age: Number }, {
  strictQuery: true
});
Character = mongoose.model('Character', schema);

const query = Character.findOne({ notInSchema: { $lt: 'not a number' } });

await query.exec();
query.getFilter(); // Empty object `{}`, Mongoose removes `notInSchema`

为了让 Mongoose 在您的 filter 中存在不在模式中的属性时抛出错误，请将 strictQuery 设置为 'throw'。

mongoose.deleteModel('Character');
const schema = new mongoose.Schema({ name: String, age: Number }, {
  strictQuery: 'throw'
});
Character = mongoose.model('Character', schema);

const query = Character.findOne({ notInSchema: { $lt: 'not a number' } });

const err = await query.exec().then(() => null, err => err);
err.name; // 'StrictModeError'
// Path "notInSchema" is not in schema and strictQuery is 'throw'.
err.message;

隐式 $in

由于模式的存在，Mongoose 知道字段应该是什么类型，因此它可以提供一些简洁的语法糖。例如，如果您忘记在非数组字段上添加 $in，Mongoose 会自动为您添加 $in。

// Normally wouldn't find anything because `name` is a string, but
// Mongoose automatically inserts `$in`
const query = Character.findOne({ name: ['Jean-Luc Picard', 'Will Riker'] });

const doc = await query.exec();
doc.name; // "Jean-Luc Picard"

// `{ name: { $in: ['Jean-Luc Picard', 'Will Riker'] } }`
query.getFilter();