I need an index that will provide me uniqueness of the field among all fields. For example, I have the document:
{
_id: ObjectId("123"),
fieldA: "a",
fieldB: "b"
}
and I want to forbid insert the document
{
_id: ObjectId("456"),
fieldA: "new value for field a",
fieldB: "a"
}
because already exists the document that has the value "a" set on field "fieldA". Is it possible?
It seems you need a multikey index with a unique constraint.
Take into account that you can only have one multikey index in each collection for this reason you have to include all the fields you like to uniqueness inside an array
{
_id: ObjectId("123"),
multikey: [
{fieldA: "a"},
{fieldB: "b"}
]
}
Give a try to this code
db.collection.createIndex( { "multikey": 1}, { unique: true } )
To query you have to code
db.collection.findOne({"multikey.fieldA": "a"}, // Query
{"multikey.fieldA": 1, "multikey.fieldB": 1}) // Projection
For more info you can take a look at embedded multikey documents.
Hope this helps.
another option is to create a document with each unique key, indexed by this unique key and perform a loop over the field of each candidate document cancelling the write if any key is found.
IMO this solution is more resource consuming, in change it gets you a list of all keys consumed in written documents.
db.collection.createIndex( { "unikey": 1}, { unique: true } )
db.collection.insertMany( {[{"unikey": "$FieldA"},{"unikey": "$FieldB"}]}
db.collection.find({"unikey": 1})
Related
Imaging we have documents like this:
{
_id: ObjectId(""),
accountId: ObjectId(""),
userId: ObjectId(""),
someOtherFieldA: ["some", "array", "values"],
someOtherFieldB: ["other", "array", "values"],
...
}
Furthermore there are multiple compound indices, ex.:
{ userId: 1, someOtherFieldA: 1, ... }
{ userId: 1, someOtherFieldB: 1, ... }
We want to shard by accountId.
Would it be enough to add a single field index for accountId, so that the existing indices still work? Or would all indices need the accountId as prefix (first part)?
When you run the sh.shardCollection() command then MongoDB automatically creates an index on the shard key field (unless such an index exist already), so you don't need to care about this question.
For example, I want to update half of data whose _id is an odd number. such as:
db.col.updateMany({"$where": "this._id is an odd number"})
Instead of integer, _id is mongo's ObejectId which be regard as hexadecimal "string". It is not supported to code as:
db.col.updateMany(
{"$where": "this._id % 2 = 1"},
{"$set": {"a": 1}}
)
so, what is the correct format?
And what if molding according to _id？
This operation can also be done using two database calls.
Get List of _id from collection.
Push only ODD _id into an array.
Update the collection.
Updating the collection:
db.collection.update(
{ _id: { $in: ['id1', 'id2', 'id3'] } }, // Array with odd _id
{ $set: { urkey : urValue } }
)
First, add an unique index to field 'items.barcode'.
db.clothes.createIndex({'items.barcode': 1}, {unique: 1});
Then, insert some documents to the clothes table.
db.clothes1.remove({});
db.clothes.insert([
{ // success
_id: '1',
items: [
{barcode: ['122', '122']},
{barcode: ['122', '124']}
]
},
{ // success
_id: '2',
items: [
{barcode: ['222', '223']},
{barcode: ['224', '225']}
]
},
{ // failed
_id: '3',
items: [
{barcode: ['122', '323']},
{barcode: ['324', '325']}
]
}
]);
Now we can see the 3rd document is inserted failed, cause the error:
'E11000 duplicate key error index: duolayimeng.clothes1.$items.barcode_1 dup key: { : "122" }'
But in the two embed documents of the 1st document, there are 3 elements of 'barcode' field are '122'.
I'm puzzled about this situation. How MongoDB decides an array type field in embed documents, like 'items.barcode', is unique or not?
That is because, an index is unique across a collection of documents.
The subdocuments are not really documents, a document is forced to have a unique field, a subdocument can not be force to be unique inside a document.
Document with id 3 is failing because other document already exists having the same unique key.
Documents with id 1 is inserting OK because there is no other document with the same unique field.
When you want to achieve uniqueness inside a document, you must implement that in the client side or modify schema and add your values inside a set using $addToSet
The unique index permits the insertion of the following document into
the collection if no other document in the collection has the a.b
value of 5:
db.collection.insert( { a: [ { b: 5 }, { b: 5 } ] } )
Here is the doc
I have two collections, customSchemas, and customdata. Besides the default _id index, I've added the following indexes
db.customData.createIndex( { "orgId": 1, "contentType": 1 });
db.customSchemas.createIndex( { "orgId": 1, "contentType": 1 }, { unique: true });
I've decided to enforce orgId on all calls, so in my service layer, every query has an orgId in it, even the ones with ids, e.g.
db.customData.find({"_id" : ObjectId("557f30402598f1243c14403c"), orgId: 1});
Should I add an index that has both _id and orgId in it? Do the indexes I have currently help at all when I'm searching by both _id and orgId?
MongoDB 2.6+ provides index intersection feature that cover your case by using intersection of index _id {_id:1} and index prefix orgId in { "orgId": 1, "contentType": 1 }
So your query {"_id" : ObjectId("557f30402598f1243c14403c"), orgId: 1} should be covered by index already.
However, index intersection is less performant than a compound index on {"_id" : 1, orgId: 1}, as it comes with an extra step (intersection of the two sets). Hence, if this is a query that you use most of the time, creating the compound index on it is a good idea.
Is there such a query that gets multiple fields, and returns which of these exists in the collection?
For example, if the collection has only:
{id : 1}
{id : 2}
And I want to know which of [{id : 1} , {id : 3}] exists in it, then the result will be something like [{id : 1}].
You are looking for the $in-operator.
db.collection.find({ id: { $in: [ 1, 3 ] } });
This will get you any documents where the id-field (different from the special _id field) is 1 or 3. When you only want the values of the id field and not the whole documents:
db.collection.find({ id: { $in: [ 1, 3 ] } }, { _id: false, id:true });
If you want to check provided key with value is present or not in collection, you can simply check by matching values and combining conditions using $or operator.
By considering id is different than _id in mongo.
You can use $or to get expected output and query will be as following.
db.collection.find({$or:[{"id":1},{"id":3}]},{"_id":0,"id":1})
If you want to match _id then use following query:
db.collection.find({$or:[{"_id":ObjectId("557fda78d077e6851e5bf0d3")},{"_id":ObjectId("557fda78d077e6851e5bf0d5")}]}