While playing with mognodb console help, I found a db.getSisterDB() method.
And I am curious what is the purpose of this method. Looking through mongodb documentation and a quick google search did not yield satisfactory results.
By typing db.getSisterDb.help generates an error and typing db.getSisterDB gives the following definition of this method:
function ( name ){
return this.getMongo().getDB( name );
}
which suggests that this is just a wrapper around getDB. My suggestion that it is used in to access databases in a replica set, but I would like to listen to a person who can give me a more thorough explanation.
In the shell, db is a reference to the current database. If you want to query against a different DB in the same mongod instance, the way to get a proper reference to it would be to use this method (which has an alias, more gender neutral getSiblingDB).
If you wanted to use the longer syntax, you could: db.getMongo().getDB(name) gets you the same thing as db.getSiblingDB(name) or db.getSisterDB(name) but the former is longer to type.
All of the above work the same way in standalone mongod as well as replica sets (and sharded clusters).
Im going to add to the accepted answer because I did not find what I wanted as a first result.
getSiblingDB exists for scripting, where the use helper is not available
getSiblingDB is the newer between the identical getSisterDB, so use sibling as getSisterDB is no longer in documentation
when used in the shell, getSiblingDB serves the purpose of getting a database without changing the db variable
Related
I didn't see any recommendation about using hyphen in field name at all
Even with #serialName it still didn't work
#SerialName("created-date")
val created_date: String,
but It worked fine with underscore (now i'm using it)
The reason i used it in the first place is because I have used a few api and most of them used hyphen and i just want to follow the common name.
If anyone know why please kindly tell me. I might be missing any docs or sth
There is a page in MongoDB documentation, I'm putting a shortcut for restrictions based on field names https://docs.mongodb.com/manual/reference/limits/#mongodb-limit-Restrictions-on-Field-Names.
MongoDB can store various different field names even you can have "space" in field name. It is not a problem for MongoDB, but once your application receives MongoDB output, it should be deserialized. I have never used kotlinx.serialization before; hence I'm just guessing. What if the problem might be coming from serialization/deserialization process. You better check kotlinx.serialization, maybe something is there.
I'm trying to call IDENT_CURRENT() against a different database without moving to that database but I can't seem to find the schema it belongs to. I tried both sys and dbo but neither worked. I've searched and searched but nowhere can I find anything relating to either it's schema or how to call it.
How do you go about running such functions on another database please? I know I can most likely create a function in that database and then call my function but I'm first trying to find out whether there's an easier way.
Thanks!
IDENT_CURRENT is a function, it doesn't belong to a schema.
You can provide it with a 3-parts identifier to a table that belongs on a different database in the same server:
SELECT IDENT_CURRENT('<Database>.<Schema>.<Table>');
However you should note that ident_current might yield wrong results.
For more information, read Aaron Bertrand's For the last time, NO, you can't trust IDENT_CURRENT().
I have a model Foo which has a field called bar.
class Foo(models.Model):
bar = models.CharField(max_length=70)
Given an existing instance of Foo whose bar field is set to 'qux', the following query returns an empty QuerySet:
Foo.objects.filter(bar__icontains="qux")
However, if I reference/save the previous instance or I create/save a new Foo, I am able to find it using a similar query.
So, how can I find old, existing records using icontains?
Djangae's documentation makes specific reference to using contains and icontains, but I see no mention of this particular behavior or how to address it. (I do see the index being added to djangaeidx.yaml) I also see nothing in the Migration documentation which makes me think I need to explicitly add an index or similar.
The answer can be found in the 0.9.10 migration guide.
In this situation, you'd need to run something like:
defer_iteration(Foo.objects.all(), Foo.save, _target="your-new-app-version")
in order to add the necessary indexes to existing records.
While this worked, it definitely feels heavy handed to me. I'd be happy to hear from anyone else who might have an alternative solution.
I'm attempting to write up a Yesod app as a replacement for a Ruby JSON service that uses MongoDB on the backend and I'm running into some snags.
the sql=foobar syntax in the models file does not seem too affect which collection Persistent.MongoDB uses. How can I change that?
is there a way to easily configure mongodb (preferably through the yaml file) to be explicitly read only? I'd take more comfort deploying this knowing that there was no possible way the app could overwrite or damage production data.
Is there any way I can get Persistent.MongoDB to ignore fields it doesn't know about? This service only needs a fraction of the fields in the collection in question. In order to keep the code as simple as possible, I'd really like to just map to the fields I care about and have Yesod ignore everything else. Instead it complains that the fields don't match.
How does one go about defining instances for models, such as ToJSON. I'd like to customize how that JSON gets rendered but I get the following error:
Handler/ProductStat.hs:8:10:
Illegal instance declaration for ToJSON Product'
(All instance types must be of the form (T t1 ... tn)
where T is not a synonym.
Use -XTypeSynonymInstances if you want to disable this.)
In the instance declaration forToJSON Product'
1) seems that sql= is not hooked up to mongo. Since sql is already doing this it shouldn't be difficult for Mongo.
2) you can change the function that runs the queries
in persistent/persistent-mongoDB/Database/Persist there is a runPool function of PersistConfig. That gets used in yesod-defaults. We should probably change the loadConfig function to check a readOnly setting
3) I am ok with changing the reorder function to allow for ignoring, although in the future (if MongoDB returns everything in ordeR) that may have performance implications, so ideally you would list the ignored columns.
4) This shouldn't require changes to Persistent. Did you try turning on TypeSynonymInstances ?
I have several other Yesod/Persistent priorities to attend to before these changes- please roll up your sleeves and let me know what help you need making them. I can change 2 & 3 myself fairly soon if you are committed to testing them.
What's the best way to keep track of unique tags for a collection of documents millions of items large? The normal way of doing tagging seems to be indexing multikeys. I will frequently need to get all the unique keys, though. I don't have access to mongodb's new "distinct" command, either, since my driver, erlmongo, doesn't seem to implement it, yet.
Even if your driver doesn't implement distinct, you can implement it yourself. In JavaScript (sorry, I don't know Erlang, but it should translate pretty directly) can say:
result = db.$cmd.findOne({"distinct" : "collection_name", "key" : "tags"})
So, that is: you do a findOne on the "$cmd" collection of whatever database you're using. Pass it the collection name and the key you want to run distinct on.
If you ever need a command your driver doesn't provide a helper for, you can look at http://www.mongodb.org/display/DOCS/List+of+Database+Commands for a somewhat complete list of database commands.
I know this is an old question, but I had the same issue and could not find a real solution in PHP for it.
So I came up with this:
http://snipplr.com/view/59334/list-of-keys-used-in-mongodb-collection/
John, you may find it useful to use Variety, an open source tool for analyzing a collection's schema: https://github.com/jamescropcho/variety
Perhaps you could run Variety every N hours in the background, and query the newly-created varietyResults database to retrieve a listing of unique keys which begin with a given string (i.e. are descendants of a specific parent).
Let me know if you have any questions, or need additional advice.
Good luck!