$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 sample.employee 中插入 3 条记录:

  1. > db.sample.employee.insert( { "id": 1, "content": { "name": "Jack", "phone": "123", "address": "1000 Market Street, Philadelphia" } } )
  2. > db.sample.employee.insert( { "id": 2, "content": [ { "name": "Tom", "phone": "456", "address": "2000 Market Street, Philadelphia" } ] } )
  3. > db.sample.employee.insert( { "id": 3, "content": { "name": "Septem", "phone": "789", "address": { "addr1": "3000 Market Street, Philadelphia", "addr2": "4000 Market Street, Philadelphia" } } } )
  4. > db.sample.employee.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.sample.employee.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.sample.employee.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.sample.employee.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.sample.employee.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).