$elemMatch

语法

  1. { <字段名>: { $elemMatch: { <子字段名>: <表达式>, ... } } }

描述

选择集合中“<字段名>”匹配指定“{ <子字段>: <表达式> … }”的记录。

其中“<表达式>”可以是值，也可以是带有匹配符的表达式，“$elemMatch”匹配符支持多层嵌套。

示例

在集合 foo.bar 中插入 3 条记录：

  1. > db.foo.bar.insert( { "id": 1, "content": { "name": "Jack", "phone": "123", "address": "1000 Market Street, Philadelphia" } } )
  2. > db.foo.bar.insert( { "id": 2, "content": [ { "name": "Tom", "phone": "456", "address": "2000 Market Street, Philadelphia" } ] } )
  3. > db.foo.bar.insert( { "id": 3, "content": { "name": "Septem", "phone": "789", "address": { "addr1": "3000 Market Street, Philadelphia", "addr2": "4000 Market Street, Philadelphia" } } } )
  4. > db.foo.bar.find()
  5. {
  6.   "_id": {
  7.     "$oid": "5a73ce416a3e18f64e000010"
  8.   },
  9.   "id": 1,
  10.   "content": {
  11.     "name": "Jack",
  12.     "phone": "123",
  13.     "address": "1000 Market Street, Philadelphia"
  14.   }
  15. }
  16. {
  17.   "_id": {
  18.     "$oid": "5a73ce476a3e18f64e000011"
  19.   },
  20.   "id": 2,
  21.   "content": [
  22.     {
  23.       "name": "Tom",
  24.       "phone": "456",
  25.       "address": "2000 Market Street, Philadelphia"
  26.     }
  27.   ]
  28. }
  29. {
  30.   "_id": {
  31.     "$oid": "5aaa25ee48bcff191e000002"
  32.   },
  33.   "id": 3,
  34.   "content": {
  35.     "name": "Septem",
  36.     "phone": "789",
  37.     "address": {
  38.       "addr1": "3000 Market Street, Philadelphia",
  39.       "addr2": "4000 Market Street, Philadelphia"
  40.     }
  41.   }
  42. }
  43. Return 3 row(s).

SequoiaDB shell 运行如下：

  • 嵌套对象匹配：
  1. > db.foo.bar.find( { "content": { $elemMatch: { "name": "Jack", "phone": "123" } } } )
  2. {
  3.   "_id": {
  4.     "$oid": "5822868a2b4c38286d000007"
  5.   },
  6.   "id": 1,
  7.   "content": {
  8.     "name": "Jack",
  9.     "phone": "123",
  10.     "address": "1000 Market Street, Philadelphia"
  11.   }
  12. }
  13. Return 1 row(s).
  • 数组匹配：
  1. > db.foo.bar.find( { "content": { $elemMatch: { "name": "Tom", "phone": "456" } } } )
  2. {
  3.   "_id": {
  4.     "$oid": "5822868a2b4c38286d000008"
  5.   },
  6.   "id": 2,
  7.   "content": [
  8.     {
  9.       "name": "Tom",
  10.       "phone": "456",
  11.       "address": "2000 Market Street, Philadelphia"
  12.     }
  13.   ]
  14. }
  15. Return 1 row(s).
  • 匹配“content”字段中子字段“phone”符合表达式“ $lte："123" ”的记录：
  1. > db.foo.bar.find( { content: { $elemMatch: { "phone" : { $lte : "123" } } } } )
  2. {
  3. "_id": {
  4.   "$oid": "5a0106e51f9b983f4600000b"
  5. },
  6. "id": 1,
  7. "content": {
  8.   "name": "Jack",
  9.   "phone": "123",
  10.   "address": "1000 Market Street, Philadelphia"
  11. }
  12. }
  13. Return 1 row(s).
  • 使用“$regex”匹配符以及嵌套的“$elemMatch”匹配符：
  1. > db.foo.bar.find( { "content" : { $elemMatch : { address : { $elemMatch: { addr1 : { $regex : ".*Philadelphia$" } } } } } } )
  2. {
  3. "_id": {
  4.   "$oid": "5a0107641f9b983f4600000d"
  5. },
  6. "id": 3,
  7. "content": {
  8.   "name": "Septem",
  9.   "phone": "789",
  10.   "address": {
  11.     "addr1": "3000 Market Street, Philadelphia",
  12.     "addr2": "4000 Market Street, Philadelphia"
  13.   }
  14. }
  15. }
  16. Return 1 row(s).