added mongo and _mongo

sheets/_mongo/comparison

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+// equals to
+db.books.find({year: {$eq: 2016}})
+
+// less than
+db.books.find({year: {$lt: 2010}})
+
+// less than or equal to
+db.books.find({year: {$lte: 2008}})
+
+// greater than
+db.books.find({year: {$gt: 2014}})
+
+// greater than or equal to
+db.books.find({year: {$gte: 2008}})
+
+// not equal to
+db.books.find({year: {$ne: 2008}})
+
+// value in
+db.books.find({year: {$in: [2008, 2016]}})
+
+// value not in
+db.books.find({year: {$nin: [2008, 2016]}})
+

sheets/_mongo/crud

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+// Insert a new document in a collection
+db.books.insert({"isbn": 9780060859749, "title": "After Alice: A Novel", "author": "Gregory Maguire", "category": "Fiction", "year":2016})
+
+// Insert multiple documents into a collection
+db.books.insert([
+    { "isbn":"9781853260001", "title": "Pride and Prejudice", "author": "Jane Austen", "category": "Fiction"},
+    {"isbn": "9780743273565", "title": "The Great Gatsby", "author": "F. Scott Fitzgerald"}
+    ])
+
+// Show all documents in the collection
+db.collection.find()
+
+// Filter documents by field value condition
+db.books.find({"title":"Treasure Island"})
+
+// Show only some fields of matching documents
+db.books.find({"title":"Treasure Island"}, {title:true, category:true, _id:false})
+
+// Show the first document that matches the query condition
+db.books.findOne({}, {_id:false})
+
+// Update specific fields of a single document that match the query condition
+db.books.update({title : "Treasure Island"}, {$set : {category :"Adventure Fiction"}})
+
+// Remove certain fields of a single document the query condition:
+// $unset
+db.books.update({title : "Treasure Island"}, {$unset : {category:""}})
+
+// Remove certain fields of all documents that match the query condition
+// $unset, {multi:true}
+db.books.update({category : "Fiction"}, {$unset : {category:""}}, {multi:true})
+
+// Delete a single document that match the query condition
+// {justOne:true}
+db.books.remove({title :"Treasure Island"}, {justOne:true})
+
+// Delete all documents matching a query condition
+db.books.remove({"category" :"Fiction"})
+
+// Delete all documents in a collection
+db.books.remove({})

sheets/_mongo/cursor

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+// Show number of documents in the collection
+db.books.find().count()
+
+// Limit the number of documents to return
+db.books.find().limit(2)
+
+// Return the result set after skipping the first n number of documents
+db.books.find().skip(2)
+
+// Sort the documents in a result set in ascending or descending order of field values
+db.books.find().sort( {title : 1} )
+// value = 1 for ascending, -1 for descending
+
+// Display formatted (more readable) result
+db.books.find({}).pretty()
+

sheets/_mongo/elements

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+// Match documents that contains that specified field
+db.books.find( {category: {$exists: true }})
+
+// Match documents whose field value is of the specified BSON data type
+db.books.find( {category: {$type: 2 }})
+

sheets/_mongo/index

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+// Create an index
+db.books.createIndex({title:1})
+// Type 1 means ascending; -1 means descending
+
+// Create a unique index
+db.books.createIndex( {isbn:1},{unique:true} )
+
+// Create a index on multiple fields (compound index)
+db.books.createIndex({title:1, author:-1})
+
+// Show all indexes in a collection
+db.books.getIndexes()
+
+// Drop an index
+db.books.dropIndex({author:-1})
+
+// Show index statistics
+db.books.stats()
+

sheets/_mongo/logical

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+// OR
+db.books.find( { $or: [{year: {$lte: 2008}}, {year: {$eq: 2016}}]} )
+
+// AND
+db.books.find( { $and: [{year: {$eq: 2008}}, {category: {$eq: "Fiction"}}]} )
+
+// NOT
+db.books.find( {$not: {year: {$eq: 2016} }})
+
+// NOR
+db.books.find( { $nor: [{year: {$lte: 2008}}, {year: {$eq: 2016}}]} )
+

sheets/_mongo/shell

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+// Show current database
+db
+
+// Select or switch database
+use mydb
+
+// Execute a JavaScript file
+load(myscript.js)
+
+// Display help
+help
+
+// Display help on DB methods
+db.help()
+
+// Display help on Collection
+db.mycol.help()
+
+// Show all databases
+show dbs
+
+// Show all collections in current database
+show collections
+
+// Show all users on current database
+show users
+
+// Show all roles on current database
+show roles
+

sheets/mongo

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+# Connect to local host on default port 27017
+mongo
+
+# Connect to remote host on specified port
+mongo --host 10.121.65.23 --port 23020
+
+# Connect to a database <host>/<database>
+mongo 10.121.65.58/mydb
+
+# Connect to a database on specified host and port
+# with this username and password
+mongo -u username -p password --port 12345 --host localhost
+
+# Run the shell after executing my-script.js
+mongo --shell my-script.js
+
+# Connect to database on specified port and host
+# and execute my-script.js after that
+mongo localhost:27017/myDatabase my-script.js
+
+# See also:
+#   MongoDB cheat sheets at /mongo/
+#   list of pages:      /mongo/:list
+#   search in pages:    /mongo/~keyword
+