lift more tutorial sections from pymongo

This commit is contained in:
Scott R. Parish 2010-03-10 16:39:58 -06:00
parent 34599280f5
commit 697c370dea
2 changed files with 95 additions and 13 deletions

2
TODO
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@ -1,6 +1,8 @@
TODO
====
+ inject _id if not given, return it
BSON
----
+ on insert/update: reject keys that start with "$" or "."

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@ -81,7 +81,7 @@ them and MongoDB will automatically create them for you.
In the below examples we'll be using the following *FullCollection*:
> import Data.ByteString.Lazy.UTF8
> let testcol = (fromString "test.haskell")
> let postsCol = (fromString "test.posts")
You can obtain a list of databases available on a connection:
@ -89,7 +89,9 @@ You can obtain a list of databases available on a connection:
You can obtain a list of collections available on a database:
> collections <- collectionNames con (fromString "test")
> cols <- collectionNames con (fromString "test")
> map toString cols
["test.system.indexes"]
Documents
---------
@ -132,39 +134,117 @@ Here's the same BSON data structure using these conversion functions:
Inserting a Document
-------------------
> insert con testcol post
To insert a document into a collection we can use the *insert* function:
> insert con postsCol post
When a document is inserted a special key, *_id*, is automatically
added if the document doesn't already contain an *_id* key. The value
of *_id* must be unique across the collection. insert() returns the
value of *_id* for the inserted document. For more information, see
the [documentation on _id](http://www.mongodb.org/display/DOCS/Object+IDs).
After inserting the first document, the posts collection has actually
been created on the server. We can verify this by listing all of the
collections in our database:
> cols <- collectionNames con (fromString "test")
> map toString cols
[u'postsCol', u'system.indexes']
* Note The system.indexes collection is a special internal collection
that was created automatically.
Getting a single document with findOne
-------------------------------------
> findOne con testcol (toBsonDoc [("author", toBson "Mike")])
The most basic type of query that can be performed in MongoDB is
*findOne*. This method returns a single document matching a query (or
*Nothing* if there are no matches). It is useful when you know there is
only one matching document, or are only interested in the first
match. Here we use *findOne* to get the first document from the posts
collection:
> findOne con postsCol []
Just [(Chunk "_id" Empty,BsonObjectId (Chunk "K\151\153S9\CAN\138e\203X\182'" Empty)),(Chunk "author" Empty,BsonString (Chunk "Mike" Empty)),(Chunk "text" Empty,BsonString (Chunk "My first blog post!" Empty)),(Chunk "tags" Empty,BsonArray [BsonString (Chunk "mongoDB" Empty),BsonString (Chunk "Haskell" Empty)]),(Chunk "date" Empty,BsonDate 1268226361.753s)]
The result is a dictionary matching the one that we inserted
previously.
* Note: The returned document contains an *_id*, which was automatically
added on insert.
*findOne* also supports querying on specific elements that the
resulting document must match. To limit our results to a document with
author "Mike" we do:
> findOne con postsCol $ toBsonDoc [("author", toBson "Mike")]
Just [(Chunk "_id" Empty,BsonObjectId (Chunk "K\151\153S9\CAN\138e\203X\182'" Empty)),(Chunk "author" Empty,BsonString (Chunk "Mike" Empty)),(Chunk "text" Empty,BsonString (Chunk "My first blog post!" Empty)),(Chunk "tags" Empty,BsonArray [BsonString (Chunk "mongoDB" Empty),BsonString (Chunk "Haskell" Empty)]),(Chunk "date" Empty,BsonDate 1268226361.753s)]
If we try with a different author, like "Eliot", we'll get no result:
> findOne con postsCol $ toBsonDoc [("author", toBson "Eliot")]
Nothing
Bulk Inserts
------------
In order to make querying a little more interesting, let's insert a
few more documents. In addition to inserting a single document, we can
also perform bulk insert operations, by using the *insertMany* api
which accepts a list of documents to be inserted. This will insert
each document in the iterable, sending only a single command to the
server:
> now <- getPOSIXTime
> :{
let new_postsCol = [toBsonDoc [("author", toBson "Mike"),
("text", toBson "Another post!"),
("tags", toBson ["bulk", "insert"]),
("date", toBson now)],
toBsonDoc [("author", toBson "Eliot"),
("title", toBson "MongoDB is fun"),
("text", toBson "and pretty easy too!"),
("date", toBson now)]]
:}
> insertMany con postsCol new_posts
* Note that *new_posts !! 1* has a different shape than the other
posts - there is no "tags" field and we've added a new field,
"title". This is what we mean when we say that MongoDB is schema-free.
Querying for More Than One Document
------------------------------------
> cursor <- find con testcol (toBsonDoc [("author", toBson "Mike")])
To get more than a single document as the result of a query we use the
*find* method. *find* returns a cursor instance, which allows us to
iterate over all matching documents. There are several ways in which
we can iterate: we can call *nextDoc* to get documents one at a time
or we can get a lazy list of all the results by applying the cursor
to *allDocs*:
> cursor <- find con postsCol $ toBsonDoc [("author", toBson "Mike")]
> allDocs cursor
You can combine these into one line:
Of course you can use bind (*>>=*) to combine these into one line:
> docs <- allDocs =<< find con testcol (toBsonDoc [("author", toBson "Mike")])
See nextDoc to modify cursor incrementally one at a time.
* Note: allDocs automatically closes the cursor when done, through nextDoc.
> docs <- find con postsCol (toBsonDoc [("author", toBson "Mike")]) >>= allDocs
* Note: *nextDoc* automatically closes the cursor when the last
document has been read out of it. Similarly, *allDocs* automatically
closes the cursor when you've consumed to the end of the resulting
list.
Counting
--------
We can count how many documents are in an entire collection:
> num <- count con testcol
> num <- count con postsCol
Or we can query for how many documents match a query:
> num <- countMatching con testcol (toBsonDoc [("author", toBson "Mike")])
> num <- countMatching con postsCol (toBsonDoc [("author", toBson "Mike")])
Range Queries
-------------