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    Type:
Bug
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    Resolution: Done
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    Priority:
Minor - P4
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    Affects Version/s: None
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    Component/s: Index Maintenance
 
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        Minor Change
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        ALL
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        None
 
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        None
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        None
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        None
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Can create indices, for example:
> coll.ensureIndex({'x.$a':1})
> coll.getIndexes()
[
	{
		"v" : 1,
		"name" : "_id_",
		"ns" : "test.t",
		"key" : {
			"_id" : 1
		}
	},
	{
		"v" : 1,
		"ns" : "test.t",
		"key" : {
			"x.$a" : 1
		},
		"name" : "x.$a_1"
	}
]
You can also create an index that contains an empty field name, i.e.: "x..a"
As you cannot save/insert/upsert a field with that name, it seems like incorrect behavior to be able to index on it.
- is related to
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SERVER-11064 Stricter validation of index key patterns during index creation and startup
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 - Closed
 
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SERVER-12070 Validate all indexes for new restrictions at startup
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 - Closed
 
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SERVER-11812 Can create indexes on invalid fields (empty, $** component)
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 - Closed
 
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- related to
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SERVER-10075 Should forbid illegal form of TTL indexes
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 - Closed
 
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