Relationships

Database tables are often related to one another. FasORM supports declarative relationships: One to One, One to Many, and Many to Many.

Relationship Descriptors

Descriptor	Relationship Type	Example Declaration
`HasMany("Target")`	One to Many (Parent)	`posts = HasMany("Post")`
`BelongsTo("Target")`	Inverse One to Many (Child)	`user = BelongsTo("User")` (Auto creates `user_id` FK)
`HasOne("Target")`	One to One (Parent)	`profile = HasOne("Profile")`
`BelongsToMany("Target", pivot="...")`	Many to Many	`roles = BelongsToMany("Role", pivot="user_roles")`

One to Many Example (User & Post)

models.py

from fasorm import Model, String, Text, HasMany, BelongsTo

class User(Model):
    name = String()
    email = String(unique=True)
    posts = HasMany("Post")

class Post(Model):
    title = String()
    body = Text()
    user = BelongsTo("User")  # Automatically creates user_id FK column

Querying One to Many Relationships

Python

# Eager-load posts with user
users = await User.with_("posts").get()
for post in users[0].posts:
    print(post.title)

# Inverse BelongsTo loading
post = await Post.with_("user").find(1)
print(post.user.name)

One to One Example (User & Profile)

models.py

class User(Model):
    name = String()
    profile = HasOne("Profile")

class Profile(Model):
    bio = Text()
    avatar_url = String()
    user = BelongsTo("User")

Many to Many Example (User & Role)

models.py

class User(Model):
    name = String()
    roles = BelongsToMany("Role", pivot="user_roles")

class Role(Model):
    name = String(unique=True)
    users = BelongsToMany("User", pivot="user_roles")

Pivot Table Creation

When defining BelongsToMany, create the pivot table (e.g. user_roles) in a migration with foreign keys pointing to both user_id and role_id.