Question

根据MongoDB文档（http://docs.mongodb.org/manual/reference/operator/projection/elemMatch/）：

{
 _id: 1,
 school: "school A",
 zipcode: 63109,
 students: [
              { name: "john", school: 102, age: 10 },
              { name: "jess", school: 102, age: 11 },
              { name: "jeff", school: 108, age: 15 }
           ]
}
{
 _id: 2,
 school: "school B",
 zipcode: 63110,
 students: [
              { name: "ajax", school: 100, age: 7 },
              { name: "achilles", school: 100, age: 8 },
           ]
}

{
 _id: 3,
 school: "school C",
 zipcode: 63109,
 students: [
              { name: "ajax", school: 100, age: 7 },
              { name: "achilles", school: 100, age: 8 },
           ]
}

{
 _id: 4,
 school: "school D",
 zipcode: 63109,
 students: [
              { name: "barney", school: 102, age: 7 },
           ]
}

发射：

schools.find（{zipcode：63109}，{students：{$ elemMatch：{school：102 }，} function（err，school）{...}

该操作返回以下文档：

{“_ id”：1，“学生”：[{“name”：“john”，“school”：102，“age”： 10}]} {“_ id”：3} {“_ id”：4，“学生”：[{“name”： “barney”，“school”：102，“age”：7}]}

但我也需要提交学校的价值......

{“_ id”：1，“学校”：“学校A”，“学生”：[{“姓名”：“约翰”，“学校”：102，“年龄”： 10}]} {“_ id”：3，“school”：“School C”} {“_ id”：4，“school”：“School D”，“students”：[{“name”： “barney”，“school”：102，“age”：7}]}

我无法找到实现这个目标的方法......

Answer 1

http://docs.mongodb.org/manual/reference/method/db.collection.find/

如果指定了投影参数，则匹配文档仅包含投影字段和_id字段。您可以可选地排除_id字段。

但是......我强迫使用字段返回：

schools.find({ zipcode: 63109}, {school: 1, students: { $elemMatch: { school: 102 } } }, function (err, school) { ...}

所有似乎都正常工作......

MongoDB（Mongoose）如何使用$ elemMatch返回所有文档字段

1 个答案: