General
Using school as the database and student as the collection.
show collections; // Show the collections which are available for this database
db.......pretty(); // Use pretty to make sure the output is formatted well
db.student.drop(); // Drop the collection
db.student.stats(); // Get the collection stats
db.student.totalIndexSize(); // Available from the stats but a short cut. It is important that the indexes fit into memory
Find
db.students.find();
db.students.find({name:'bob'});
db.students.find({name:'bob'}).count(); // Return the number of matches for this find
db.students.find({age:{$gt:15}}); // Find students with age greater than 15
db.students.find({age:{$gt:15, $lt:18}}); // Find students with age greater than 15 and less than 18
db.students.find({name:{$regex : 'q'}, email : {$exists : true}}); // Find all the students whose name includes a 'q' and who have an email
db.students.find({$or:[{age:15}, {age:16}]}); // Students with age 15 or 16
db.students.find({pets:{$in:['dog','cat']}}); // Students with a pet dog or cat
db.students.find({pets:{$all:['dog','cat']}}); // Students with a pet dog and cat
db.students.find({pets:{$in:['dog','cat']}}); // Students with a pet dog or cat
db.students.find({pets:{$all:['dog','cat']}}); // Students with a pet dog and cat
db.students.find({age:{$gt:15}}, {"_id":0, name:1, age:1}); // Projection which changes the data fields that are returned.
db.students.find( {_id:4}, {pets: {$slice:2}}); // Return the first two elements of the pet array only
db.students.find( {_id:4}, {pets: {$slice:2}}); // Return the first two elements of the pet array only
db.students.find().sort({age:1}); // Sort by age ascending
var cursor = db.students.find();
cursor.next(); // A cursor is returned if the find query is allocated to a variable
db.students.find({$text : {$search : 'bob fred'}}); // Do a search on a text index for all the documents containing 'bob' or 'fred' (case insensitive)
db.students.find({address:{$near: [x,y]}}); // Returns values based on a 2d index in increasing distance often used with a limit(n)
db.students.find({address:{
$near: {
$geometry : {
type : "Point",
coordinates : [long, lat]},
$maxDistance : 2000
}
}
}); // Returns values based on a 2dspherical index in increasing distance often used with a limit(n). Searches for Lat & Long with a max distance
Insert
db.students.insert({name: 'Fred', age:17, results:[78.8, 89.9]});Delete / Remove
db.students.remove({}); // Removes all documents from the collection
db.students.remove({name:'Fred'}, {justOne:true}); // Removes the first 'Fred' entry found
Update
db.country.update({pop:{$gt:2000000}}, {$set: {large_country:'true'}}, {multi:true}); // Update all countries which have a population greater than 2Mil to have a new flag saying large_country=true
db.country.update({_id:'Japan'},{pop='30000000', lang='Japanese'}); // All other entries in the document are removed.
db.country.update({_id:'Japan'}, {$set : {countryCode:'JP'}}); // Add the countryCode = 'JP' to the document with _id = 'Japan'
db.country.update({_id:'Japan'}, {$unset : {countryCode:1}}); // Remove the countryCode key from the document with _id = 'Japan'
db.country.update({_id:'Japan'}, {$push : { languages: "Japanese"}}); // Adds 'Japanese' to the list of languages for 'Japan'
db.country.update({_id:'GB'}, {_id:'GB', languages:'English', pop:50000000}, {upsert:true}); // Looks to update the object but will insert it if it can't be found
Indexes
Index creation is run in the foreground by default and will lock the collection that is being indexed so that no read or write request will be published.
db.student.createIndex({name:1, class:-1}); (1 = ascending, -1 = descending)
db.student.createIndex({name:1}, {unique:true}); // Create a unique index
db.student.createIndex({name:1}, {unique:true, sparse:true}); // Create a unique index which is also sparse. Used when there could be null / missing values from a document.
db.student.createIndex({name:1}, {background:true}); // Create this index in the background without locking the collection
db.student.createIndex({'name.result':1}); // Create an index into the array of result embedded documents
db.student.createIndex({'name':'text'}); // Create an index into the array of name embedded documents
db.student.createIndex({'location':'2d'}); // Create an index based on a 2d location where 'location' is an array of two coordinates
db.student.createIndex({'location':'2dsphere'}); // Create an index based on a 2d spherical location where 'location' is an array of two coordinates latitude and longitude.
db.student.dropIndex({name:1});
Explain
Use the explain option to see which indexes are being used and other data.db.student.explain().find({name:1}); // Explain the information about this find request
db.student.explain("executionStats").find({name:1});
Aggregation
Use the aggregation frame work to do groupings, counts, sums, averages etc$group
db.student.aggregate([{$group:{_id : "$surname", count:{$sum:1}}}]); // Count the number of students with the same surname
db.student.aggregate([{$group:{_id : {name : "$name", surname : "$surname"}, exam_avg : {$avg:"$result"}}}; // Use an _id as a document to identify the student. Then average the exam marks
db.products.aggregate([{$group:{_id: $manufacturer, categories:{$addToSet:"$category"}}}]); // Build an array of the categories which each manufacturer has. This builds a set so doesn't create duplicates in the array
db.products.aggregate([{$group:{_id: $manufacturer, categories:{$push:"$category"}}}]); // Build an array of the categories which each manufacturer has. $push allows duplicates in the array.
db.products.aggregate([{$group:{_id: $manufacturer, categories:{$max:"$price"}}}]); // Find the max price of a manufacturer product.
db.products.aggregate([{$group:{_id: $manufacturer, categories:{$min:"$price"}}}]); // Find the min price of a manufacturer product.
db.students.aggregate([
{$group:{_id:{class_id:"$class_id", student_id:"$student_id"}, student_avg : {$avg:"$score"}}},
{$group:{_id:"$_id.class_id", class_avg: {$avg:"$student_avg"}}}]); // Average each students marks in a class, then average all the single
db.student.aggregate([{$sort: {category : 1, price : 1}}, {$group:{ _id:"$category", cheapest :{$first: "$price"}}}]); // Sort by category & price and return the first value = cheapest per category
$projectAllows you to 'reshape' a document eg add keys, remove keys. To keep a key put $keyName:1 otherwise the key will be removed - with the exception of _id which needs to be explicitly excluded.
db.products.aggregate([{$project :{
_id:0,
'maker':{$toLower:$manufacturer}, // Create a new key with the Lower Case of the manufacturer
'details':{category:"$category",
price:{$multiply : [$price, 10]}}, // Create new document of category and 10xprice
item: $name // Keep the name as a new key called 'item'
}}]);
$match
db.student.aggregate([{$match:{category : "tablet"}}]); // Match values - very similar to find()
$sort
db.student.aggregate([{$sort:{price: 1}}]); // Sort by price - very similar to sort()
$skip
db.student.aggregate([{$sort:{price: 1}, $skip : 10}]); // Skip the first 10 records - only use with a sort first
$limit
db.student.aggregate([{$sort:{price: 1}, $limit : 5 }]); // Only return 5 records - only use with a sort first
$unwind
db.student.aggregate([{$unwind : "$classes"}]); // Unwind the classes that the students have done
db.getProfilingLevel();
db.getProfilingStatus();
db.setProfilingLevel(1, 4); // 1 is the level and 4 is the threshold ms for queries
db.system.profile.find(); // Find queries which have been profiled because they took too long.
db.system.profile.find({millis:{$gt:1000}}).sort({ts:-1}); // Find all the queries that took longer than 1 second sorted in timestamp descending order
mongostat is useful and is similar to iostat on a linux box.
mongotop # // samples the database every # seconds and prints out an overview of where mongo is slow.
rs.status();
rs.conf(); // Show the current configuration of the replica set
rs.slaveOk(); // Allow queries on a secondary in a replica set
rs.help(); // Get help on the replica set commands
Create
Create a replication set called "rs1" with a particular data path and listening on a particular port.
mongod --replSet rs1 --logpath "1.log" --dbpath /data/rs1 --port 27017 --fork
config = { _id : "rs1" , members:[
{_id : 0, host : "192.168.1.1.27017"},
{_id : 1, host : "192.168.1.2.27017"}, ]}
rs.initiate(config);
Profiling
With profiling on the db.system collection gets profiling information about queries which take longer than the threshold specified.db.getProfilingLevel();
db.getProfilingStatus();
db.setProfilingLevel(1, 4); // 1 is the level and 4 is the threshold ms for queries
db.system.profile.find(); // Find queries which have been profiled because they took too long.
db.system.profile.find({millis:{$gt:1000}}).sort({ts:-1}); // Find all the queries that took longer than 1 second sorted in timestamp descending order
mongostat is useful and is similar to iostat on a linux box.
mongotop # // samples the database every # seconds and prints out an overview of where mongo is slow.
Replication
Generalrs.status();
rs.conf(); // Show the current configuration of the replica set
rs.slaveOk(); // Allow queries on a secondary in a replica set
rs.help(); // Get help on the replica set commands
Create
Create a replication set called "rs1" with a particular data path and listening on a particular port.
mongod --replSet rs1 --logpath "1.log" --dbpath /data/rs1 --port 27017 --fork
config = { _id : "rs1" , members:[
{_id : 0, host : "192.168.1.1.27017"},
{_id : 1, host : "192.168.1.2.27017"}, ]}
rs.initiate(config);
