What is onetomany and manytoone

The difference between One-to-many, Many-to-one and Many-to-Many is:

One-to-many vs Many-to-one is a matter of perspective. Unidirectional vs Bidirectional will not affect the mapping but will make difference on how you can access your data.

In Many-to-one the many side will keep reference of the one side. A good example is "A State has Cities". In this case State is the one side and City is the many side. There will be a column state_id in the table cities.
In unidirectional, Person class will have List<Skill> skills but Skill will not have Person person. In bidirectional, both properties are added and it allows you to access a Person given a skill( i.e. skill.person).

In One-to-Many the one side will be our point of reference. For example, "A User has an Addresses". In this case we might have three columns address_1_id, address_2_id and address_3_id or a look up table with unique constraint on user_id and address_id.
In unidirectional, a User will have Address address. Bidirectional will have an additional List<User> users in the Address class.

In Many-to-Many members of each party can hold reference to arbitrary number of members of the other party. To achieve this a look up table is used. Example for this is the relationship between doctors and patients. A doctor can have many patients and vice versa.

Similar codes

16 votes259 views2 answers
Auto clicker in python
Python
2 votes245 views1 answer
Get stats from list
Python
9 votes250 views2 answers
Python readlines without n
Python
0 vote271 views1 answer
How to check if two strings are same in Python
Python
0 vote257 views1 answer
Python extract list from string
Python
3 votes271 views2 answers
Django radio button
Python Django
0 vote240 views1 answer
Python close a socket
Python
19 votes241 views1 answer
Python left string
Python
0 vote271 views1 answer
Histogram for categorical data with plotly
Python
1 vote275 views1 answer
Django queryset multiple filters
Python