I need to select transactions with the same type as a given transaction. And I need to check that it doesn't return all transactions with the nil type.
With ActiveRecord I can easily write:
given_transaction = Transaction.first
needed_transactions = Transaction.where('type != nil and type = ?', given_transaction.type)
and all works
when I try to write the same thing with mongoid:
needed_transactions = Transaction.where(:type => given_transaction.type, :type.ne => nil)
It generates the following query:
"query"=>{:type=>{"$ne"=>"planned"}}
In other words, mongoid ignores the first check and only uses the last check on the field.
I tried "all_of", "all_in", "and" — and still can't find the working solution.
Maybe I am doing something wrong... My world is going upside down because of this... :(((
From the fine manual:
All queries in Mongoid are Criteria, which is a chainable and lazily evaluated wrapper to a MongoDB dynamic query.
And looking at the Criteria docs for where we see a bunch of examples with a single condition. But remember the chainability mentioned above. Perhaps you're looking for this:
needed_transactions = Transaction.where(:type => given_transaction.type).where(:type.ne => nil)
The Criteria#and docs might make good reading as well:
Adds another simple expression that must match in order to return results. This is the same as Criteria#where and is mostly here for syntactic sugar.
MONGOID
# Match all people with last name Jordan and first name starting with d.
Person.where(last_name: "Jordan").and(first_name: /^d/i)
MONGODB QUERY SELECTOR
{ "last_name" : "Jordan", "first_name" : /^d/i }
I have to admit that I don't understand why you're checking :type twice like that though; if given_transaction.type.nil? is possible then you could deal with that without even querying your database.
And BTW, with ActiveRecord you'd want to say this:
Transaction.where('type is not null and type = ?', given_transaction.type)
As far as the strange query you're getting is concerned, when you do this:
Transaction.where(:type => given_transaction.type, :type.ne => nil)
Mongoid ends up trying to build a Hash with two values for the :type key:
{ :type => 'planned' }
{ :type => { :$ne => nil } }
and somehow it ends up replacing the nil with 'planned'. I don't know the internal details of Mongoid's where or the methods it patches into Symbol, I'm just backtracking from the observed behavior.
Related
I'm using Mongoid to access a MongoDB database, however I'm running into an odd problem. It seems like I can only query for records using find_by, as find will always return nil:
invoices = Invoice.find({})
p "invoices"
p invoices
puts ''
invoice = Invoice.find_by({ _id: <ObjectId> })
p "invoice"
p invoice
puts ''
The second query using find_by will return a single record. According to the documentation, find should be returning every record that satisfies the query.
Does anyone have an idea what could be causing this?
Be careful not to confuse the Moped syntax with the Mongoid syntax. For Mongoid, the docs describe the find method:
Find a document or multiple documents by their ids. Will raise an error by default if any of the ids do not match
If you really want every record, Invoice.all can do the trick. (Also be careful with your find_by method. The Mongoid syntax varies from mongo's a bit, so you don't have to have the curlies around your params.)
I'm building a advanced search functionality and, thanks to the help of some ruby fellows on SO, I've been already able to combine AND and OR conditions programmatically on different fields of the same class.
I ended up writing something similar to the accepted answer mentioned above, which I report here:
query = criteria.each_with_object({}) do |(field, values), query|
field = field.in if(values.is_a?(Array))
query[field] = values
end
MyClass.where(query)
Now, what might happen is that someone wants to search on a certain field with multiple criteria, something like:
"all the users where names contains 'abc' but not contains 'def'"
How would you write the query above?
Please note that I already have the regexes to do what I want to (see below), my question is mainly on how to combine them together.
#contains
Regex.new('.*' + val + '.*')
#not contains
Regex.new('^((?!'+ val +').)*$')
Thanks for your time!
* UPDATE *
I was playing with the console and this is working:
MyClass.where(name: /.*abc.*/).and(name: /^((?!def).)*$/)
My question remains: how do I do that programmatically? I shouldn't end up with more than two conditions on the same field but it's something I can't be sure of.
You could use an :$and operator to combine the individual queries:
MyClass.where(:$and => [
{ name: /.*abc.*/ },
{ name: /^((?!def).)*$/ }
])
That would change the overall query builder to something like this:
components = criteria.map do |field, value|
field = field.in if(value.is_a?(Array))
{ field => value }
end
query = components.length > 1 ? { :$and => components } : components.first
You build a list of the individual components and then, at the end, either combine them with :$and or, if there aren't enough components for :$and, just unwrap the single component and call that your query.
I am new to mongodb/mongomapper and can't find an answer to this.
I have a mongomapper class with the following fields
key :author_id, Integer
key :partecipant_ids, Array
Let's say I have a "record" with the following attributes:
{ :author_id => 10, :partecipant_ids => [10,15,201] }
I want to retrieve all the objects where the partecipant with id 15 is involved.
I did not find any mention in the documentation.
The strange thing is that previously I was doing this query
MessageThread.where :partecipant_ids => [15]
which worked, but after (maybe) some change in the gem/mongodb version it stopped working.
Unfortunately I don't know which version of mongodb and mongomapper I was using before.
In the current versions of MongoMapper, this will work:
MessageThread.where(:partecipant_ids => 15)
And this should work as well...
MessageThread.where(:partecipant_ids => [15])
...because plucky autoexpands that to:
MessageThread.where(:partecipant_ids => { :$in => [15] })
(see https://github.com/jnunemaker/plucky/blob/master/lib/plucky/criteria_hash.rb#L121)
I'd say take a look at your data and try out queries in the Mongo console to make sure you have a working query. MongoDB queries translate directly to MM queries except for the above (and a few other minor) caveats. See http://www.mongodb.org/display/DOCS/Querying
how do you retrieve an array of IDs in Mongoid?
arr=["id1","id2"]
User.where(:id=>arr)
You can do this easily if you are retrieving another attribute
User.where(:nickname.in=>["kk","ll"])
But I am wondering how to do this in mongoid -> this should be a very simple and common operation
Remember that the ID is stored as :_id and not :id . There is an id helper method, but when you do queries, you should use :_id:
User.where(:_id.in => arr)
Often I find it useful to get a list of ids to do complex queries, so I do something like:
user_ids = User.only(:_id).where(:foo => :bar).distinct(:_id)
Post.where(:user_id.in => user_ids)
Or simply:
arr = ['id1', 'id2', 'id3']
User.find(arr)
The above method suggested by browsersenior doesn't seem to work anymore, at least for me. What I do is:
User.criteria.id(arr)
user_ids = User.only(:_id).where(:foo => :bar).map(&:_id)
Post.where(:user_id.in => user_ids)
The solution above works fine when amount of users is small. But it will require a lot of memory while there are thousands of users.
User.only(:_id).where(:foo => :bar).map(&:_id)
will create a list of User objects with nil in each field except id.
The solution (for mongoid 2.5):
User.collection.master.where(:foo => :bar).to_a.map {|o| o['_id']}
I have an application that manages documents called Notes. Like a blog, Notes can be searched for matches against one or more Tags, which are contained in a Note.Tags collection property. A Tag has Name and ID properties, and matches are made against the ID. A user can specify multiple tags to match against, in which case a Note must contain all Tags specified to match.
I have a very complex LINQ query to perform a Note search, with extension methods and looping. Quite frankly, it has a real code smell to it. I want to rewrite the query with something much simpler. I know that if I made the Tag a simple string, I could use something like this:
var matchingNotes = from n in myNotes
where n.Tags.All(tag => searchTags.Contains(tag))
Can I do something that simple if my model uses a Tag object with an ID? What would the query look like. Could it be written in fluent syntax? what would that look like?
I believe you can find notes that have the relevant tags in a single LINQ expression:
IQueryable<Note> query = ... // top part of query
query = query.Where(note => searchTags.All(st =>
note.Tags.Any(notetag => notetag.Id == st.Id)));
Unfortunately there is no “fluent syntax” equivalent for All and Any, so the best you can do there is
query = from note in query
where searchTags.All(st =>
note.Tags.Any(notetag => notetag.Id == st.Id))
select note;
which is not that much better either.
For starters see my comment; I suspect the query is wrong anyway! I would simplifiy it, by simply enforcing separately that each tag exists:
IQueryable<Note> query = ... // top part of query
foreach(var tagId in searchTagIds) {
var tmpId = tagId; // modified closures...
query = query.Where(note => note.Tags.Any(t => t.Id == tmpId));
}
This should have the net effect of enforcing all the tags specified are present and accounted for.
Timwi's solution works in most dialects of LINQ, but not in Linq to Entities. I did find a single-statement LINQ query that works, courtesy of ReSharper. Basically, I wrote a foreach block to do the search, and ReSharper offered to convert the block to a LINQ statement--I had no idea it could do this.
I let ReSharper perform the conversion, and here is what it gave me:
return searchTags.Aggregate<Tag, IQueryable<Note>>(DataStore.ObjectContext.Notes, (current, tag) => current.Where(n => n.Tags.Any(t => t.Id == tag.Id)).OrderBy(n => n.Title));
I read my Notes collection from a database, using Entity Framework 4. DataStore is the custom class I use to manage my EF4 connection; it holds the EF4 ObjectContext as a property.