Wildcard Index Restrictions通配符索引限制

Incompatible Index Types or Properties不兼容的索引类型或属性

Wildcard indexes do not support the following index types or properties:通配符索引不支持以下索引类型或属性：

• Compound复合

• TTL

• text

• 2d (Geospatial)

• 2dsphere (Geospatial)

• Hashed

• Unique

Unsupported Query and Aggregation Patterns不支持的查询和聚合模式

Field does not exist字段不存在

Wildcard indexes are sparse and do not index empty fields. 通配符索引是稀疏的，不对空字段进行索引。Wildcard indexes therefore cannot support querying for documents where a field does not exist.因此，通配符索引无法支持查询不存在字段的文档。

For example, consider a collection inventory with a wildcard index on product_attributes. 例如，考虑在product_attributes上具有通配符索引的集合inventory。The wildcard index cannot support the following queries:通配符索引无法支持以下查询：

db.inventory.find( {"product_attributes" : { $exists : false } } )

db.inventory.aggregate([
  { $match : { "product_attributes" : { $exists : false } } }
])

Field is equal to a document or an array字段等于文档或数组

Wildcard indexes generate entries for the contents of a document or array, and not the document/array itself. 通配符索引为文档或数组的内容生成条目，而不是文档/数组本身。Wildcard indexes therefore cannot support exact document/array equality matches. 因此，通配符索引无法支持精确的文档/数组相等匹配。Wildcard indexes can support querying where the field equals an empty document {}.通配符索引可以支持查询字段等于空文档{}的位置。

For example, consider a collection inventory with a wildcard index on product_attributes. 例如，考虑在product_attributes上具有通配符索引的集合inventory。The wildcard index cannot support the following queries:通配符索引无法支持以下查询：

db.inventory.find({ "product_attributes" : { "price" : 29.99 } } )
db.inventory.find({ "product_attributes.tags" : [ "waterproof", "fireproof" ] } )

db.inventory.aggregate([{
  $match : { "product_attributes" : { "price" : 29.99 } }
}])

db.inventory.aggregate([{
  $match : { "product_attributes.tags" : ["waterproof", "fireproof" ] } }
}])

Field is not equal to a document or array字段不等于文档或数组

Wildcard indexes generate entries for the contents of a document or array, and not the document/array itself. 通配符索引为文档或数组的内容生成条目，而不是文档/数组本身。Wildcard indexes therefore cannot support exact document/array inequality matches.因此，通配符索引无法支持精确的文档/数组不等式匹配。

For example, consider a collection inventory with a wildcard index on product_attributes. 例如，考虑在product_attributes上具有通配符索引的集合inventory。The wildcard index cannot support the following queries:通配符索引无法支持以下查询：

db.inventory.find( { $ne : [ "product_attributes", { "price" : 29.99 } ] } )
db.inventory.find( { $ne : [ "product_attributes.tags",  [ "waterproof", "fireproof" ] ] } )

db.inventory.aggregate([{
  $match : { $ne : [ "product_attributes", { "price" : 29.99 } ] }
}])

db.inventory.aggregate([{
  $match : { $ne : [ "product_attributes.tags", [ "waterproof", "fireproof" ] ] }
}])

Array Field is equal or not equal to null数组字段等于或不等于null

If a given field is an array in any document in the collection, wildcard indexes cannot support queries for documents where that field is equal or not equal to null.如果给定字段是集合中任何文档中的数组，则通配符索引无法支持查询该字段等于或不等于null的文档。

For example, consider a collection inventory with a wildcard index on product_attributes. 例如，考虑在product_attributes上具有通配符索引的集合inventory。The wildcard index cannot support the following queries if product_attributes.tags is an array in any document in the collection:如果product_attributes.tags是集合中任何文档中的数组，则通配符索引无法支持以下查询：

db.inventory.find( { "product_attributes.tags": { $ne: null } } )

db.inventory.find( { "product_attributes.tags": null } )

db.inventory.aggregate([{
  $match : { "product_attributes.tags": { $ne: null } }
}])

db.inventory.aggregate([{
  $match : { "product_attributes.tags": null }
}])

Field is equal to null字段等于null

Wildcard indexes cannot support queries for documents where a field is equal to null. 通配符索引不能支持对字段等于null的文档进行查询。The query { $eq: null } matches all documents where the field is null or missing. 查询{ $eq: null }匹配字段为null或缺失的所有文档。Wildcard are sparse, meaning they do not index the documents where the indexed field is missing, and therefore cannot support a match on null.通配符是稀疏的，这意味着它们不会对缺少索引字段的文档进行索引，因此无法支持null匹配。

For example, consider a collection inventory with a wildcard index on product_attributes. 例如，考虑在product_attributes上具有通配符索引的集合inventory。The wildcard index cannot support the following queries:通配符索引无法支持以下查询：

db.inventory.find( { "product_attributes.price": { $eq: null } } )

db.inventory.aggregate([{
   $match : { "product_attributes.price": { $eq: null } }
}])

Sharding分片

You cannot shard a collection using a wildcard index. Create a non-wildcard index on the field or fields you want to shard on. 不能使用通配符索引对集合进行分片。在要对其进行分片的一个或多个字段上创建一个非通配符索引。For more information on shard key selection, see Shard Keys.有关分片关键帧选择的详细信息，请参阅分片关键帧。