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joplin notion extension/Web Development/NOSQL/mongodb/Shell.md
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joplin notion extension/Web Development/NOSQL/mongodb/Shell.md
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Shell
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Type `mongosh` in terminal to start the shell
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- `show databases/dbs` : to show databases
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- `show collections` : to show collections
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- `use test2` : switch to test2 database. if test2 doesnt exist it will still switch to it. Once the collection is created in non existent database then that database will be created.
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- cls : to clear screen
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- creating variable
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`var name="yoshi"`
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then type name in shell it will return `yoshi`
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`name = "mario"`
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then typing name in shell will return `mario`
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- exit : to exit shell
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**Creating document**
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- First add collection using
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`db.createCollection('col1')` this
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- Inserting document
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`db.col1.insertOne({title : "The Color of Magic", author : "Terry Pratchett"})`
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We dont have `col2` but if we try to insert document in this collection then this connection will be created
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`db.col2.insertOne({title : "title1"})`
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for inserting multiple
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`db.col1.insertMany([{title: "The light fantastic"}, {title: "title2"}])`
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**Finding Documents**
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- Getting all documents
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`db.col1.find()` this is similar to `select * from col2` in sql.
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- Using filters in find method
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- `db.col1.find({author : "Terry Pratchett",
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title :
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"The Color of Magic"})`
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This will print those document with given fields values
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its equal to `select * from col1 where author = 'Terry Pratchett' and title = 'The Color of Magic'`
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- `db.col1.find({author : "Terry Pratchett"}, {title: 1, author : 1})`
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To specify what field we want instead of getting whole document we can specify that in 2nd parameter of find method.
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this is similar to
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`select title,author from col1 where author = 'Terry Pratchett'`
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To get some field but with no filter
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`db.col1.find({}, {title: 1, author : 1})`
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just pass empty object as 1st parameter for that
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- `db.col1.findOne({_id: ObjectId('66590a00d3c92df2cd286ea0')}`
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to find one document and to pass fields which are keys basically as it will just find first document which matched property.
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**Sorting and Limiting Data**
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- `db.col1.find({author : "Terry Pratchett"}).count()`
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We can chain methods like this. after getting results, count method will return the count of them
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- `db.col1.find().limit(2)`
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this will return the first 2 results
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- to get 11th to 20th results and not first 20 results use
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`db.col1.find().skip(10).limit(10)`
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When you chain skip() and limit(), the method chaining order does not affect the results. The server always applies the skip operation based on the sort order before it applies the limit on how many documents to return.
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The following code example shows different chaining orders for skip() and limit() that always produce the same query results for the same data set:
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```js
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db.myColl.find().sort({_id: 1}).skip(3).limit(6);
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db.myColl.find().sort({_id: 1}).limit(6).skip(3);
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```
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- `db.col1.find().sort({title: 1}).limit(2)`
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this will sort the documents by title in ascending and return the first 2 results
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in order to sort by descending order use
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`db.col1.find().sort({title: -1}).limit(2)`
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**Nested Documents**
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- Instead of creating separate collection we can add them as nested documents too to reduce the complexity too
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Query
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```js
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db.books.insertOne({
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title: "The Way of Kings",
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author: "Brandon Sanderson",
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rating: 9,
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pages: 320,
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genres: ["fantasy"],
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reviews: [{
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name: "Yoshi",
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body: "Great book!!!"
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},
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{
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name: "mario",
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body: "So so"
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}
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]
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})
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db.books.insertMany(
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[{title: "The Light Fantastic",
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author: "Terry Pratchett",
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pages: 250,
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rating: 6,
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genres: ["fantasy", "magic"],
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reviews: [{name:"luigi", body: "it was pretty good"}, {name: "bowser", body: "loved it!!"}]}, {title: "The Name of the Wind", "author": "Patrick Rothfuss", page: 500, "rating": 10, genres: ["fantasy"], review: [{name: "peach", body: "one of my favs"}]},
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{title: "The Color of Magic",
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"author": "Terry Pratchett",
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page: 350,
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"rating": 8,
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genres: ["fantasy", "magic"],
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review: [{name: "luigi", body: "it was ok"}, {name: "bowser", body: "really good book"}]},
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{title: "1984",
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"author": "George Orwell",
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page: 300,
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"rating": 6,
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genres: ["sci-fi", "dystopian"], review: [{name: "peach", body: "not my cup of tea"}, {name: "mario", body: "meh"}]}
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])
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```
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**Operations and Complex Queries**
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- All operators begin with `$` sign
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- gt : greater than
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`db.books.find({rating : {$gt : 8}})`
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All books with rating greater than 8
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- gte : greater than or equal to
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- lt : lesser than
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- lte : lesser than or equal to
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- or
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`db.books.find({$or : [ {rating : 7}, {rating: 9} ]})`
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this will return those books whose rating is either 7 or 9.
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`db.books.find({ $or : [{rating : 7}, {author: "Terry Pratchett" } ] })`
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- last example
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`db.books.find( {$or : [{pages: {$lt : 300}}, {pages: {$gt: 400} } ]} )`
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this will return books with pages less than 300 and pages greater than 400.
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- for accessing nested objects
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```js
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db.col1.insertOne(
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{
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"obj": {
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"data": "lorem"
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}
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}
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)
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```
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`db.col1.find( { "obj.data": "lorem" } )`
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- Summary
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```
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- Name
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= Description
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$eq
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Matches values that are equal to a specified value.
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$gt
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Matches values that are greater than a specified value.
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$gte
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Matches values that are greater than or equal to a specified value.
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$in
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Matches any of the values specified in an array.
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$lt
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Matches values that are less than a specified value.
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$lte
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Matches values that are less than or equal to a specified value.
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$ne
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Matches all values that are not equal to a specified value.
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$nin
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Matches none of the values specified in an array.
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Logical
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- Name
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= Description
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$and
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Joins query clauses with a logical AND returns all documents that match the conditions of both clauses.
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$not
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Inverts the effect of a query expression and returns documents that do not match the query expression.
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$nor
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Joins query clauses with a logical NOR returns all documents that fail to match both clauses.
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$or
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Joins query clauses with a logical OR returns all documents that match the conditions of either clause.
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```
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**in and nin operator**
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- in :
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`db.books.find({rating : {$in : [7,8,9] }})` : return results whose ratings are either of the values in array. Same can be done with `or`
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`db.books.find({$or : [ {rating: 7},{rating: 8},{rating: 9} ] })`
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- nin :
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`db.books.find({rating : {$nin : [7,8,9] }})` : return results whose ratings are neither of the values in array. Same can be done with `nor`
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`db.books.find({$nor : [ {rating: 7},{rating: 8},{rating: 9} ] })`
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**Querying Arrays**
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- Match found
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`db.books.find({genres: "fantasy"})`
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this will return the documents whose field genre contains fantasy in its array. genre may be only fantasy or it can have more genres too but `fantasy` must be included.
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- Only match
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As genre is array so to get the only match
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`db.books.find({genres: ["fantasy"]})`
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this will return documents with field containing this value which is `fantasy` only. we can have magic too so it will return those which contains values `fantasy` and `magic` too.
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eg 2: `db.books.find({genres: ["fantasy","magic"]})`
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- Match found for given set(all operator)
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Only match will only return those with specified but if we want to include those with given set(they can have more but given set must be included) then
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`db.books.find({genres: {$all: ["fantasy", "sci-fi"]} })`
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- Match found of either of given values
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for example if we need those which contains atleast magic or atleast sci-fi in one of them
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`db.books.find({ $or: [ {genres: "magic"}, {genres : "sci-fi"} ] })`
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- Matching nested documents
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review field contains documents itself. Suppose we wanna query those documents whose review have documnets with field name and we want specific name too like 'luigi'(documnets where reviews is posted by user 'luigi') then
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`db.books.find({"review.name": "luigi"})`
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**Deleting Documents**
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- `db.books.deleteOne({_id : ObjectId('66592602d3c92df2cd286ea5')})`
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this will delete one document with the given `_id` value. we can have different field too but since id is unique so it is recommended.
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- `db.books.deleteMany({author : "Terry Pratchett"})`
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Unlike deleteOne which will delete only one document and stop its search, this will delete all the documents containing the given value of field
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**Updating Documents**
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- `db.books.updateOne( {_id : ObjectId('66592602d3c92df2cd286ea5') }, {$set : {rating : 8, pages : 350}} )`
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set operator is used to change the values of fields of document whose id is ` ObjectId('66592602d3c92df2cd286ea5')`.
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- `db.books.updateMany( {author : "Terry Pratchett" }, {$set : {author : "Terry Pratchet"}} )`
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to update records of given field. unlike updateOne it will check for every records and wont stop after first match is found.
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- inc operator
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`db.books.updateOne( {_id: ObjectId('66592602d3c92df2cd286ea2')}, {$inc : {pages : 2} } )`
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unlike set it doesnt replace but increment it so in case we dont know the value and wanna increment it then we can use this
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To decrement it we can pass just negative number like `-2`
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- push and pull
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to add or delete contents in array
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`db.books.updateOne( {_id: ObjectId('66592602d3c92df2cd286ea2')}, {$pull : {genres : "fantasy"} } )`
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to delete `fantasy` from array of genres
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`db.books.updateOne( {_id: ObjectId('66592602d3c92df2cd286ea2')}, {$push : {genres : "fantasy"} } )`
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to add `fantasy` in array of genres
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- each
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with push and pull we can only do it for one element of array. for multiple elements we have to each operator
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`db.books.updateOne( {_id: ObjectId('66592602d3c92df2cd286ea2')}, {$push : {genres : {$each : ["1","2"] } } } )`
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this will push '1' and '2' in array of genres field.
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- pullAll
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to do same with pull we cant use each but need to use pullAll
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`db.books.updateOne( {_id: ObjectId('66592602d3c92df2cd286ea2')}, {$pullAll : {genres : ["1","2"] } } )`
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- to update nested document
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To update the name from "Yoshi" to "Yosh" in the MongoDB document, you can use the updateOne() method with a filter to match the document and an update operation to modify the nested field within the "reviews" array. Here's an example of how you can do it using MongoDB's shell:
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```js
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db.books.updateOne(
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{ "reviews.name": "Yoshi" }, // Filter to match the document containing the review with name "Yoshi"
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{ $set: { "reviews.$.name": "Yosh" } } // Update operation to set the name to "Yosh"
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)
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```
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So `reviews.$.name` refers to the "name" field within the matched element of the "reviews" array. It ensures that only the specific review that matched the query condition (in this case, the review with the name "Yoshi") will have its "name" field updated to "Yosh".
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so $ is positional operator
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Similary to change array element use
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```js
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db.books.updateOne(
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{ "genres": "fantasy" }, // Filter to match the document containing "fantasy" in the genres array
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{ $set: { "genres.$": "fantas" } } // Update operation to set the value to "fantas"
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)
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```
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### Indexes
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- By default when we find a document through a filter which is not id it scans all documents. Id field is already indexed. But we can also set another field's values as index too by creating a separate index
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- Its simlar to caching/indexing in order to get results faster
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- One thing to be noted that creating index is not appropriate always when the field is write heavy instead of read heavy bcz whenever value is modified or new document is added indexed needs to be updated so it can be costly too if field is write heavy.
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- Checking evaluation stats
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`db.books.find({ rating : 8 }).explain('executionStats')`
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this will return totalDocsExamined as number of all documents
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- Creating index
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`db.books.createIndex({rating : 8})`
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- Print the list of indexed
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`db.books.getIndexes()`
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Now when checking evaluation stat it will return totalDocsExamined as number of documents where rating of 8 exist
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- Deleting index
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`db.books.dropIndex({rating : 8})`
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### Improrting and exporting documents
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- To export collection named `books` from database named `new2`
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`mongoexport --db new2 --collection books --out ~/Desktop/upload/books.json`
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- To import collection named `books` from to database `new3`
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`mongoimport --db new3 --collection books --file ~/Desktop/upload/books.json`
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- to export whole database named `new2`
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`mongodump -d new2 -o ~/Desktop/upload/new2`
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- to import database from the dump folder
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`mongorestore -d new4 ~/Desktop/upload/new2/new2/`
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- Exporting with certain query
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`mongosh new2 --quiet --eval 'DBQuery.shellBatchSize = 2000; db.books.find({}).limit(2000).toArray()' > books.json`
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as DbQuery.shellBatcjSize is depreciated so use this
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`mongosh new2 --quiet --eval 'config.set("displayBatchSize", 2000); db.books.find({}).limit(2000).toArray()' > books.json`
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or with a script file containing query
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file containing following statement
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`printjson(db.books.find({}).limit(2000).toArray() )`
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so use this command
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`mongosh new2 --eval 'load("./Desktop/upload/query.js")'`
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**for remote databases use**
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- `mongoexport --uri "mongodb+srv://<username>:<password>@testcluster.7kxguvp.mongodb.net/" --db sample_mflix --collection comments -o ~/Desktop/upload/comments.json`
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