MongoDb

Question 1

How can you add a custom ID field to a record if you don’t want to use the default?

Answer 1

Use _id: “custom content” for the field

Question 2

What cmd line command will start the Mongodb server and allow cmd line input?

Answer 2

mongo

Question 3

Command to Delete a single document from a collection ?

Answer 3

db.posts.deleteOne( { “transparency” : “several” } );

Removes the first that matches the criteria.

Question 4

Update a single document and create (or overwrite) a single field.

Answer 4

db.posts.updateOne( { “airport”: “Logan” }, { $set: { “marker”: “delete” }} );

Question 5

what type of update or delete commands can the selection criteria just be { } ?

Answer 5

updateMany and deleteMany

Question 6

show a way to delete all records in a collection regardless of whether they have fields in common or not.

Answer 6

db.posts.deleteMany( { } );

Question 7

show insertMany using a text array.

Answer 7

db.posts.insertMany( [ { … } ]

where a JSON text file is insert (can be many lines)

Question 8

show insertMany as you would enter fields individually

Answer 8

db.posts.insertMany( { “a”: “value1”}. { “b”: “another” }, …

Question 9

list current databases

Answer 9

show dbs

NOTE: a new database won’t appear until you add (insert) at least one record OR at least create a new collection.

Question 10

create a new database

Answer 10

use myNewDb

Question 11

use an existing database

Answer 11

use myDatabase

Question 12

Add a new collection to the current database

Answer 12

db.createCollection(“name”, { options } )
or
db.createCollection(“name”);

Options:
capped	Boolean	(Optional) If true, enables a capped collection. Capped collection is a fixed size collection that automatically overwrites its oldest entries when it reaches its maximum size. If you specify true, you need to specify size parameter also.

autoIndexId Boolean (Optional) If true, automatically create index on _id field.s Default value is false.

size number (Optional) Specifies a maximum size in bytes for a capped collection. If capped is true, then you need to specify this field also.

max number (Optional) Specifies the maximum number of documents allowed in the capped collection.

Question 13

What is the result of the following syntax:

db.col.update{ {_id: Object:”sdfsd”} { fieldA: “xyzzy” } }

Answer 13

The entire record is replaced with ONE field in this case fieldA.
If $set is added, then it will only update the one fieldA without touching the other fields.

Question 14

How to delete a database.

Answer 14

use databaseToDelete

db.dropDatabase()

Question 15

show how to replace an existing record.

Answer 15

db.flights.replaceOne(
{_id: ObjectId(“5f41477288e0fe4c33f4c928”)},
{ “departureAirport”: “MUC”, “arrivalAirport”: “SFO”, “aircraft”: “Airbus A380”, “distance”: 12000, “intercontinental”: true } )

Question 16

show how to output all the records (and not stop after the first 20) as an array.

Answer 16

db.passengers.find().toArray()

Question 17

Show how to send all records to a function that will print all records in json format.

Answer 17

db.passengers.find().forEach( (passData) =>
{ printjson(passData) }

This can output to a language specific function(s); see Mongodb drivers documentation