ormar/docs/models/methods.md

Model methods

!!!tip Main interaction with the databases is exposed through a QuerySet object exposed on each model as Model.objects similar to the django orm.

To read more about **quering, joining tables, excluding fields etc. visit [queries][queries] section.**

Each model instance have a set of methods to save, update or load itself.

Available methods are described below.

pydantic methods

Note that each ormar.Model is also a pydantic.BaseModel, so all pydantic methods are also available on a model, especially dict() and json() methods that can also accept exclude, include and other parameters.

To read more check pydantic documentation

load

By default when you query a table without prefetching related models, the ormar will still construct your related models, but populate them only with the pk value. You can load the related model by calling load() method.

load() can also be used to refresh the model from the database (if it was changed by some other process).

track = await Track.objects.get(name='The Bird')
track.album.pk # will return malibu album pk (1)
track.album.name # will return None

# you need to actually load the data first
await track.album.load()
track.album.name # will return 'Malibu'

load_all

load_all(follow: bool = False, exclude: Union[List, str, Set, Dict] = None) -> Model

Method works like load() but also goes through all relations of the Model on which the method is called, and reloads them from database.

By default the load_all method loads only models that are directly related (one step away) to the model on which the method is called.

But you can specify the follow=True parameter to traverse through nested models and load all of them in the relation tree.

!!!warning To avoid circular updates with follow=True set, load_all keeps a set of already visited Models, and won't perform nested loads on Models that were already visited.

So if you have a diamond or circular relations types you need to perform the loads in a manual way.

```python
# in example like this the second Street (coming from City) won't be load_all, so ZipCode won't be reloaded
Street -> District -> City -> Street -> ZipCode
```

Method accepts also optional exclude parameter that works exactly the same as exclude_fields method in QuerySet. That way you can remove fields from related models being refreshed or skip whole related models.

Method performs one database query so it's more efficient than nested calls to load() and all() on related models.

!!!tip To read more about exclude read exclude_fields

!!!warning All relations are cleared on load_all(), so if you exclude some nested models they will be empty after call.

save

save() -> self

You can create new models by using QuerySet.create() method or by initializing your model as a normal pydantic model and later calling save() method.

save() can also be used to persist changes that you made to the model, but only if the primary key is not set or the model does not exist in database.

The save() method does not check if the model exists in db, so if it does you will get a integrity error from your selected db backend if trying to save model with already existing primary key.

track = Track(name='The Bird')
await track.save() # will persist the model in database

track = await Track.objects.get(name='The Bird')
await track.save() # will raise integrity error as pk is populated

update

update(_columns: List[str] = None, **kwargs) -> self

You can update models by using QuerySet.update() method or by updating your model attributes (fields) and calling update() method.

If you try to update a model without a primary key set a ModelPersistenceError exception will be thrown.

To persist a newly created model use save() or upsert(**kwargs) methods.

track = await Track.objects.get(name='The Bird')
await track.update(name='The Bird Strikes Again')

To update only selected columns from model into the database provide a list of columns that should be updated to _columns argument.

In example:

class Movie(ormar.Model):
    class Meta:
        tablename = "movies"
        metadata = metadata
        database = database

    id: int = ormar.Integer(primary_key=True)
    name: str = ormar.String(max_length=100, nullable=False, name="title")
    year: int = ormar.Integer()
    profit: float = ormar.Float()

terminator = await Movie(name='Terminator', year=1984, profit=0.078).save()

terminator.name = "Terminator 2"
terminator.year = 1991
terminator.profit = 0.520

# update only name
await terminator.update(_columns=["name"])

# note that terminator instance was not reloaded so
assert terminator.year == 1991

# but once you load the data from db you see it was not updated
await terminator.load()
assert terminator.year == 1984

!!!warning Note that update() does not refresh the instance of the Model, so if you change more columns than you pass in _columns list your Model instance will have different values than the database!

upsert

upsert(**kwargs) -> self

It's a proxy to either save() or update(**kwargs) methods described above.

If the primary key is set -> the update method will be called.

If the pk is not set the save() method will be called.

track = Track(name='The Bird')
await track.upsert() # will call save as the pk is empty

track = await Track.objects.get(name='The Bird')
await track.upsert(name='The Bird Strikes Again') # will call update as pk is already populated

delete

You can delete models by using QuerySet.delete() method or by using your model and calling delete() method.

track = await Track.objects.get(name='The Bird')
await track.delete() # will delete the model from database

!!!tip Note that that track object stays the same, only record in the database is removed.

save_related

save_related(follow: bool = False, save_all: bool = False, exclude=Optional[Union[Set, Dict]]) -> None

Method goes through all relations of the Model on which the method is called, and calls upsert() method on each model that is not saved.

To understand when a model is saved check save status section above.

By default the save_related method saved only models that are directly related (one step away) to the model on which the method is called.

But you can specify the follow=True parameter to traverse through nested models and save all of them in the relation tree.

By default save_related saves only model that has not saved status, meaning that they were modified in current scope.

If you want to force saving all of the related methods use save_all=True flag, which will upsert all related models, regardless of their save status.

If you want to skip saving some of the relations you can pass exclude parameter.

Exclude can be a set of own model relations, or it can be a dictionary that can also contain nested items.

!!!note Note that exclude parameter in save_related accepts only relation fields names, so if you pass any other fields they will be saved anyway

!!!note To read more about the structure of possible values passed to exclude check Queryset.fields method documentation.

!!!warning To avoid circular updates with follow=True set, save_related keeps a set of already visited Models on each branch of relation tree, and won't perform nested save_related on Models that were already visited.

So if you have circular relations types you need to perform the updates in a manual way.

Note that with save_all=True and follow=True you can use save_related() to save whole relation tree at once.

Example:

class Department(ormar.Model):
    class Meta:
        database = database
        metadata = metadata

    id: int = ormar.Integer(primary_key=True)
    department_name: str = ormar.String(max_length=100)


class Course(ormar.Model):
    class Meta:
        database = database
        metadata = metadata

    id: int = ormar.Integer(primary_key=True)
    course_name: str = ormar.String(max_length=100)
    completed: bool = ormar.Boolean()
    department: Optional[Department] = ormar.ForeignKey(Department)


class Student(ormar.Model):
    class Meta:
        database = database
        metadata = metadata

    id: int = ormar.Integer(primary_key=True)
    name: str = ormar.String(max_length=100)
    courses = ormar.ManyToMany(Course)

to_save = {
            "department_name": "Ormar",
            "courses": [
                {"course_name": "basic1",
                 "completed": True,
                 "students": [
                     {"name": "Jack"},
                     {"name": "Abi"}
                 ]},
                {"course_name": "basic2",
                 "completed": True,
                 "students": [
                     {"name": "Kate"},
                     {"name": "Miranda"}
                 ]
                 },
            ],
        }
# initializa whole tree
department = Department(**to_save)

# save all at once (one after another)
await department.save_related(follow=True, save_all=True)

department_check = await Department.objects.select_all(follow=True).get()

to_exclude = {
    "id": ...,
    "courses": {
        "id": ...,
        "students": {"id", "studentcourse"}
    }
}
# after excluding ids and through models you get exact same payload used to
# construct whole tree
assert department_check.dict(exclude=to_exclude) == to_save

!!!warning save_related() iterates all relations and all models and upserts() them one by one, so it will save all models but might not be optimal in regard of number of database queries.