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--- mongodb [2012/11/19 22:45]
mantis [Introduction]
+++ mongodb [2012/11/22 10:51] (current)
mantis [Indizes]
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+====== Introduction ======
+From [[http://www.mongodb.org/|the hp]]: "MongoDB (from "humongous") is a scalable, high-performance, open source NoSQL database. Written in C++, features"
+  * Document-Oriented Storage (JSON-style documents with dynamic schemas offer simplicity and power)
+  * Full Index Support (Index on any attribute)
+  * Replication & High Availability (Mirror across LANs and WANs)
+  * Auto-Sharding (Scale horizontally without compromising functionality)
+  * Querying
+  * Fast In-Place Updates
+  * Map/Reduce
+  * GridFS
+  * Commercial Support
+This page aims to be a MongoDB **"hello world"** example, for more info read
+  * [[MongoDBCookBook]]
+  * [[MongoDBAdmin]]
+===== Differences to traditional DBMS =====
+MongoDB does not support transactions. [[http://www.mongodb.org/display/DOCS/Atomic+Operations|Atomic operations]] are supported.
+====== Getting started ======
+<code bash>
+sudo apt-get install mongodb
+</code>
+will pull in all dependencies, install and start the database.
+If required, adjust settings in /etc/mongodb.conf (like IP binding or port)
+===== Start/stop database =====
+<code bash>
+sudo service mongodb stop
+sudo service mongodb start
+</code>
+===== Login to database =====
+An easy way is the [[http://www.mongodb.org/display/DOCS/mongo+-+The+Interactive+Shell|mongo]] interactive shell.
+In a terminal, type
+<code bash>
+mongo
+</code>
+This connects to database "test".
+====== Usage examples ======
+The information below comes from the [[http://www.mongodb.org/display/DOCS/Manual|MongoDB manual]]
+===== Use a specific database =====
+To use a specific database, say "accounts", login to mongo and issue
+<code bash>
+>use accounts
+</code>
+If database "accounts" does not exist yet, it will be created.
+List all existing databases:
+<code bash>
+>show dbs
+</code>
+===== Collections =====
+MongoDB [[http://www.mongodb.org/display/DOCS/Collections|collections]] can be compared to RDBS tables. Collections are named groupings of documents.
+Login to a specific database and list existing collections:
+<code java>
+>use accounts
+>show collections
+</code>
+As with databases, the first time you access a collection, it will be automatically be created for you.
+===== Insert documents =====
+As mentioned before, MongoDB is document-oriented. Whereas you think of //rows// in RDBMS, you think of [[http://www.mongodb.org/display/DOCS/Documents|documents]] in MongoDB.
+More specifically, MongoDB documents are in JSON format.
+Insert one document
+<code bash>
+> db.transactions.save({"name":"alice","type":"withdrawal", "amount": 30})
+</code>
+or bulk insert (supported in shell since v2.2)
+<code bash>
+>db.transactions.save([{"name":"alice","type":"deposit", "amount": 500}, {"name":"alice","type":"withdrawal", "amount": 50}, {"name":"bob","type":"withdrawal", "amount": 20}, {"name":"bob","type":"withdrawal", "amount": 60}])
+</code>
+===== Update =====
+Change transaction type to "deposit" where name=bob and amount 60
+<code java>
+> db.transactions.update({"name":"bob", "amount":60}, {$set : {"type":"deposit"}})
+</code>
+===== Delete documents =====
+<code java>
+db.transactions.drop() 	//drop the entire transactions collection
+db.transactions.remove() //remove all objects from the collection
+db.transactions.remove( { name : "sara" } )  //remove objects from the collection where name is sara
+</code>
+===== Retrieve data =====
+Get all documents
+<code java>
+> db.transactions.find()
+</code>
+==== With WHERE clause====
+Alice's money transactions:
+<code java>
+> db.transactions.find({"name" : "alice"})
+</code>
+==== Only specific fields ====
+Show only type and amount fields
+<code java>
+> db.transactions.find({}, {"type":true, "amount":true, "_id":false})
+</code>
+==== Limit result to x rows ====
+<code java>
+> db.transactions.find({}, {}).limit(2)
+</code>
+==== Sort results ====
+sort by name ascending, amount descending
+<code java>
+> db.transactions.find( {},{}).sort({"name":1,"amount":-1})
+</code>
+==== Indizes ====
+Run ensureIndex(), which builds the index ONLY if it does not already exist.
+<code java>
+db.transactions.ensureIndex({"name":true});
+</code>
+View existing indizes
+<code java>
+db.transactions.getIndexes()
+</code>
+The [[http://docs.mongodb.org/manual/core/indexes/|manual]] has more details.
+===== Simple analyses =====
+==== Count lines ====
+<code java>
+> db.transactions.count()
+// or with a WHERE clause
+> db.transactions.count({"name":"alice"})
+</code>
+==== Calculate sum ====
+How much did all users withdraw?
+<code java>
+> db.transactions.group( {
+   "key": {"name":true} ,
+   "cond": {"type":"withdrawal"},
+   "reduce": function (obj,prev) { prev.csum += obj.amount; },
+   "initial": { csum: 0 }
+}  )
+</code>
+==== Calculate average ====
+==== Distinct values ====
+<code java>
+> db.transactions.distinct("name")
+</code>
+==== Analyse query ====
+Use [[http://www.mongodb.org/display/DOCS/Explain#Explain-millis|explain()]] to get statistics about a query, e.g. check "millis" for the query runtime in milliseconds.
+**NOTE: during the execution of explain(), the actual query is being run!** So if the query takes lots of time, explain() will take a long time, too.
+<code java>
+> db.transactions.find({},{"name":true, "amount":"true"}).explain()
+{
+	"cursor" : "BasicCursor",
+	"isMultiKey" : false,
+	"n" : 6,
+	"nscannedObjects" : 6,
+	"nscanned" : 6,
+	"nscannedObjectsAllPlans" : 6,
+	"nscannedAllPlans" : 6,
+	"scanAndOrder" : false,
+	"indexOnly" : false,
+	"nYields" : 0,
+	"nChunkSkips" : 0,
+	"millis" : 0,
+	"indexBounds" : {
+	},
+	"server" : "ankh:27017"
+}
+</code>

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