I've read the docs of mongodb and get to know that if I want to do text search I should use create index. But can I create index for each data during insert process? If I can, how should I do?
The index is created once for a collection, i.e. for text index do this
db.yourCollection.createIndex({yourText:"text"})
The index is updated automatically on every insert operation. You don't have to do this manually but have it in mind. This is what makes insert operations expensive. The more indexes you have the longer it takes to insert a document and update all of them.
If you want a link to the documentation, this topic is faced here.
Related
I would like to get a list of items from an external resource periodically and save them into a collection.
There are several possible solutions but they are not optimal, for example:
Delete the entire collection and save the new list of items
Get all items from the collection using "find({})" and use it to filter out existing items and save those that do not exist.
But a better solution will be to set a unique key and just do kind of "update or insert".
Right now on saving items the unique key already exists I will get an error
is there a way to do it at all?
**upsert won't do the work since it's updating all items with the same value so it's actually good for a single document only
I have a feeling you can achieve what you want simply by using the "normal" insertMany with the ordered option set to false. The documentation states that
Note that one document was inserted: The first document of _id: 13
will insert successfully, but the second insert will fail. This will
also stop additional documents left in the queue from being inserted.
With ordered to false, the insert operation would continue with any
remaining documents.
So you will get "duplicate key" exceptions which, however, you can simply ignore in your case.
Is there a way I can find the last inserted document and the field, i.e. _id or id such that I can increment and use when inserting a new document?
The issue is that I create my own id count, but I do not store this, now I've deleted records, I cannot seem to add new records because I am attempting to use the same id.
There is no way to check insertion order in MongoDB, because the database does not keep any metadata in the collections regading the documents.
If your _id field is generated server-side then you need to have a very good algorithm for this value in order to provide collision avoidance and uniqueness while at the same time following any sequential constraints that you might have.
My requirement is to update or add an array field into large collection. I've index on filed "Roles". While update this collection it is taking arounf 3 miniutes .. Before creating index on "role" filed it was taking less than 40 sec to update/add fileds in the collection. We need the index to read the collection . But while update it makes trouble. Is it possible to disable index while update in mongodb.. Is there any funtions available with mongo? My mongodb version is 2.6.5
Please advice.
In Mongodb Indexes are updated synchronously with the insert/update. There is no way to pause the update of Indexes.
If your indexes are already created then you have two options
Drop the index and recreate the index, but it will have the following impacts
Queries executed at the time of the insert/update is happening will miss the index.
Rebuilding index is too expensive
Wait for the index to be updated
Queries will not use partially-built indexes: the index will only be usable once the index build is complete.
Source: http://docs.mongodb.org/manual/core/index-creation/
That means your index will block any query on the field/collection as long as the index is not complete. Therefore your have no chance but waiting for the index to be updated after adding new data.
Maybe try using another index.
I'm beginner with mongoDB. i want to know is there any way to load predefined schema to mongoDB? ( for example like cassandra that use .cql file for this purpose)
If there is, please intruduce some document about structure of that file and way for restoring.
If there is not, how i can create an index only one time when I create a collection. I think it is wrong if i create index every time I call insert method or run my program.
p.s: I have a multi-threaded program that every thread insert and update my mongo collection. I want to create index only one time.
Thanks.
To create an index on a collection you need to use ensureIndex command. You need to only call it once to create an index on a collection.
If you call ensureIndex repeatedly with the same arguments, only the first call will create an index, all subsequent calls will have no effect.
So if you know what indexes you're going to use for your database, you can create a script that will call that command.
An example insert_index.js file that creates 2 indexes for collA and collB collections:
db.collA.ensureIndex({ a : 1});
db.collB.ensureIndex({ b : -1});
You can call it from a shell like this:
mongo --quiet localhost/dbName insert_index.js
This will create those indexes on a database named dbName on your localhost. It's worth noticing that if your database and/or collections are not yet created, this will create both the database and the collections for which you're adding the indexes.
Edit
To clarify a little bit. MongoDB is schemaless so you can't restore it's schema.
You can only create indexes and collections (by using createCollection helper).
MongoDB is basically schemaless so there is no definition of a schema or namespaces to be restored.
In the case of indexes, these can be created at any time. There does not need to be a collection present or even the required fields for the index as this will all be sorted out as the collections are created and when documents are inserted that matches the defined fields.
Commands to create an index are generally the same with each implementation language, for example:
db.collection.ensureIndex({ a: 1, b: -1 })
Will define the index on the target collection in the target database that will reference field "a" and field "b", the latter in descending order. This will happen even if the collection or even the database does not exist as yet, or in fact will establish a blank namespace in that case.
Subsequent calls to the same index creation method do not actually re-create the index. Where the same index is specified to one that already exists it is effectively skipped as a "no-operation".
As such, you can simply feed all your required index creation statements at application startup and anything that is not already present will be created. Anything that already exists will be left alone.
I want to do a batch insert in mongodb , but if the record exists already it should replace it with the new one.There is update command but its not possible to do it in batch.Any idea whether it is possible? I am using java api.
Thanks
Edit:
As my collection size is not very huge, i am renaming the collection with drop Target option set to true and creating a new collection with this data.As i cant risk deleting and creating a new collection this is better, but it will be awesome if there is replace into equivalent.
If you are having any primary key in your collection, then it will replace automatically.Make sure your documents have _id key.
Look at mongodb document:
Shorthand for insert/update is save - if _id value set, the record is updated if it exists or inserted if it does not; if the _id value is not set, then the record is inserted as a new one.
in http://mongodb.github.io/node-mongodb-native/markdown-docs/insert.html