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MongoDB.md

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MongoDB

Notes

  • There are components:
    1. Server
    2. Client
  • Each document has a unique column known as _id created automatically by mongodb
  • Commands in MongoDB are case sensitive
  • With a single command you can insert a document in the collection and the MongoDB creates that collection on the fly
  • To Exit from mongoShell use exit

Useful Commands

  • To Create a database, run use as use database-name
  • To Check the database available in system show dbs
  • To drop database, first use databasename and followed by db.dropDatabase()
  • To Create a collection, run db.createCollection(collectionname,constraints) as db.createCollection("teachers",{capped:true,size:9232768})
  • To show collections available in a database, run show collections
  • To drop a collection, run db.collection_name.drop()
  • To list the inserted documents, run db.collection_name.find()
  • To Insert one document, run db.collection_name.insertOne({all key value pairs})
  • An Example to insert many documents is
db.orders.insert([{ _id: 1, cust_id: "abc1", ord_date: ISODate("2012-11-02T17:04:11.102Z"), status: "A", amount: 50 },
{ _id: 2, cust_id: "xyz1", ord_date: ISODate("2013-10-01T17:04:11.102Z"), status: "A", amount: 100 },
{ _id: 3, cust_id: "xyz1", ord_date: ISODate("2013-10-12T17:04:11.102Z"), status: "D", amount: 25 },
{ _id: 4, cust_id: "xyz1", ord_date: ISODate("2013-10-11T17:04:11.102Z"), status: "D", amount: 125 },
{ _id: 5, cust_id: "abc1", ord_date: ISODate("2013-11-12T17:04:11.102Z"), status: "A", amount: 25 }])
  • To Find documents based on some conditions, run db.collection_name.find(dictionary-of-parameters)
  • The In Operator from RDBMS is used in MongoDB as db.collection_name.find(status: {$in: ["A","D"]})
  • To Update the documents we have
    1. db.collection.updateOne(<filter>,<update>,<options>) -> update the document that is found first
    2. db.collection.updateMany(<filter>,<update>,<options>) -> Update all the documents matching the given condition
    3. db.collection.update(<filter>,<update>,<options>)
  • An Example of Update is
db.inventory.updateOne(
... {item:"paper"},
... {
... $set: {"size.uom":"cm",status:"P"},
... $currentDate: {lastModified:true}
... }
... )
  • To replace the document, run db.collection_name.replaceOne(<filter>,{new key value pair}), this will replace one document which matches the given filter condition while the Object Id remains the same
  • To delete all documents from a collection, db.collection_name.deleteMany()
  • To delete documents with specific criteries, db.collection_name.deleteMany(<filter>) as db.collection_name.deleteMany({status:"A"})
  • To delete record with the first occurence of matching filter, use db.collection_name.deleteOne()

Options in Collections

  1. capped:type:boolean
    • Takes only true and false
    • Once the collection reaches that limit, it starts overwriting old entries
    • On specifying Capped to true, we need to define the size parameter
  2. size:type:number
    • This specifies the max size of collection
  3. max:type:number
    • This specifies the max number of documents a collection can hold
    • If max is 100, then after 100 documents, new entries will be overwrited from 1 position
  4. autoIndexId:type:boolean
    • The default value is false
    • It automatically creates index on the field _id for each document

Operators

  1. $eq
  2. $gt
  3. $gte
  4. $in
  5. $it
  6. $ite
  7. $ne -> all values not equal to specific value
  8. $nin -> match none of the values specified in array
  9. $and ->db.collection_name.find({$and: [{col1:val1},{col2:{$lt:$val2}}]}) and , also represents and
  10. $not
  11. $nor
  12. $or -> db.collection_name.find({$or: [{col1:val1},{col2:{$lt:$val2}}]})
  13. $exist -> Matches documents that have the specifeid field, db.records.find({field_name:{$exists:true}})
  14. $type -> Selects documents if a field is of the specified type
db.inventory.find({status:"A",qty:{$lt:30}})

Projection

  • Used to represent only the columns that you want to display
  • This is basically another parameter to be passed to find method
  • db.collection_name.find({parameters of conditions},{columns to display})
  • Display is referred as 1 and 0 not to display
  • Example: db.inventory.find({status:"D"},{item:1,status:1})

Aggregare Functions

  • This is an example of aggregate functions
db.collection_name.aggregate(
    [
        {$match: {status:"A}},
        {$group: {_id:"cust_id",total: {$sum: "$amount"}}}
    ]
)
  • It is modeled on the concept of data processing pipelines

Indexes

  • Indexes are special data structures that store a small portion of the collections data set in an easy to traverse form
  • The index stores the value of a specified field or set of fields, ordered by the value of the field
  • The ordering of the index entries supports efficient equality matches and range-based query operations
  • MongoDB by defaut uses _id for Index
  • We can not drop _id from a document
  • To create index, db.collection.createIndex(<key and index type specification>,<options>)
  • Create a single key descending index on the name field: db.collection.createIndex({name:-1})
  • The Default name of an index is the concatenation of key_value pair
  • Index is used by Database-engine for executing the Search queries