5 rules, why we use Foreign Keys in our databases:

1. Relationships establishment - we can create relations between tables, and even inner join relation within one table between two records
2. Data Integrity - for example, you can create an order with client_id for client which does not exist in the database
3. Data consistency and accuracy - when foreign key is defined, it restricts the values that can be inserted or updated in the referencing column
4. Data querying - thanks to the foreign keys we can retrieve data from multiple tables faster and easier
5. Data maintenance - it helps cascading updates and deletions, preventing locks mechanisms

MonkeyPatching in Ruby is actually extremely easy to understand and use.

We can monkey patch any ruby class, and this is how to do it.

Simple code to run one spec multiple times:

for i in `seq 10`; do rspec spec; done

This is how i usually create a simple Docker container for Python code:

This is the simple instruction on how to download the dump file with sql database and import it to the local postgreqsql database

Redis is quite easy to use, it's just basic key->value database which can be used in many different cases.

Let's assume, we already have Redis server setup in our application, and only need to use it.