Database

Converting Rails from sqlite3 to PostgreSQL

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Your mod 3 and 4 projects were probably done using sqlite3. If you did your mod5 project in sqlite3, tsk tsk!

  • edit your Gemfile
  • comment out sqlite and add gem pg
  • Screen Shot 2018-06-13 at 11.51.49 AM
  • run “bundle install”
  • edit config/database.yml
  • Change your databases names, as below.
  • Screen Shot 2018-06-13 at 12.01.58 PM
  • run rake db:create
  • run rake db:migrate
  • run rake db:seed(if you have a seed file)
  • Now test your app, and you are now using Postgres!

How do I know that it worked?

  • Go to the little Postgres elephant, and click him
  • Press stop
  • Screen Shot 2018-06-13 at 12.11.01 PM
  • If your site does not work, then you migrated successfully. Refresh your browser if needed
  • Now start up Postgres so you can continue developing!

Drop a database from postgres

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in bash

type psql

\list or \l to list your database

terminate any connections by using the following command. example if databse named YourDatabase

select pg_terminate_backend(pid) from pg_stat_activity where datname=’YourDatabase’;

*use procid instead of pid for older versions of postgres

DROP DATABASE “YourDatabase”;

Now your database is gone.

https://stackoverflow.com/questions/7073773/drop-postgresql-database-through-command-line for reference

MONGODB: What is a projection?

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A projection is when you search for documents in MongoDB but only get back the fields that you request.

example records   {name: “Tom”, age: “35”, zipcode: “10003”,_id:778789754}

using projection for name and zipcode: {name: “Tom”,  zipcode: “10003”}

 

var mongo = require(“mongodb”).MongoClient;
var url = “mongodb://localhost/addressbook”;
var collectionName = “friends”;
mongo.connect(url,function(err,db){
if(err) console.log(err)//throw err;
else{
var collection = db.collection(collectionName);
collection.find({},{name: 1, age: 0,_id:0,zipcode: 0}).toArray( function(err,documents){
if(err) console.log(err)//throw err;
else{
console.log(documents)
}
});

db.close();
}
})