this post was submitted on 16 Jun 2024
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understanding many2one, one2many and many2many relationshit (lemmy.ca)
submitted 4 months ago by kionite231@lemmy.ca to c/programming@programming.dev
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Hii,

I am new to database thing so I am trying to wrap my head around it.

  1. many2one: so in this relationship you will have more than one record in one table which matches to only one record in another table. something like A <-- B. where (<--) is foreign key relationship. so B will have a column which will be mapped to more than one record of A.

  2. one2many: same as many2one but instead now the foreign key constrain will look something like A --> B.

  3. many2many: this one is interesting because this relationship doesn't make use of foreign key directly. to have this relationship between A and B you have to make a third database something like AB_rel. AB_rel will hold values of primary key of A and also primary key of B. so that way we can map those two using AB_rel table.

tell me if I got something wrong :) give me some suggestion <3

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[–] hperrin@lemmy.world 15 points 4 months ago (1 children)

One to many: my primary key is other table’s foreign keys.

Many to one: other table’s primary key is my foreign keys.

Many to many: my primary key and other table’s primary key are all foreign keys that connect each other in some other table.

So yeah, you’ve got it right. :)

[–] RagnarokOnline@programming.dev 3 points 4 months ago

This is probably the most straightforward explanation. In many-to-many, I usually have a helper table standing in between which holds the foreign keys