status: #doc 
Tags: #python/django 
links:
Date: 2024-07-11
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A model is the single, definitive source of information about your data. It contains the essential fields and behaviors of the data you’re storing. Generally, each model maps to a single database table.

# structure

- each model is class in models.py in our app folder ex:
```python
from django.db import models

class Person(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
```
class name is name of the table and each field is name of column in db
for [more](https://docs.djangoproject.com/en/5.0/topics/db/models/)

## fields

we have different fields for different data types most useful are :

- CharField : for text with fixed max length 
- TextField : for text with flexible max length 
- BooleanField : for true or false value
- IntegerField : for An integer. Values from **-2147483648** to **2147483647**
- FloatField : A floating-point number represented in Python by a `float` instance.
for [more Field](https://docs.djangoproject.com/en/5.0/ref/models/fields/#field-types)

- for optional fields that can be blank use blank=true
- for default value to be inserted inside a field use default="my_value"
```python
class Person(models.Model):
    name = models.CharField(max_length=30,default="not_found")
    address = models.textfield(blank=true)
    is_alive = models.booleanfield(default=true)
```
# migration 

as we do our changes to django project we need to apply these changes to our database we use 2 command for this 
- makemigration
	make migration plan no change in db
```sh
python manage.py makemigration
```
- migrate
	make change to db based on plan in last command
```sh
python manage.py migrate
```

# interaction with model

for interaction directly use python shell, use this command in project folder with env active:

```sh
python manage.py shell
```

## import

before any interaction first you must import your model, use this in your views or first in py shell

```python
# my_app is name of app that you chose in begining
# person is name of model you want to import
from my_app.models import person
```

## crud operation

### create 
with model in structure section in mind 
- with crate method
```python
person.objects.create(first_name="max",last_name="ford")
```
- with save method
``` python
from my_app.models import person

# Create an instance of the model
someone = person(first_name="max",last_name="ford")
# Save the object to the database
someone.save()
```
### read
- you can save queryset in variable
```python
people = person.objects.all()
print(people)
```

- all
```python
person.objects.all()
```
- filter
```python
person.objects.filter(first_name="mohammad")
```
- Single Record
```python
person.objects.get(first_name="mohammad",last_name="karimi")
```

> [!note] 
>  `get()` raises a 'DoesNotExist' exception if no matching record is found and a 'MultipleObjectsReturned' exception if more than one record is found.

### update
- Update with save method (variable)
```python
someone = person.objects.get(id=1)
someone.first_name = "ali"
someone.save()
```

Update Using `update()
```python
# we can also use all() and get()
person.objects.filter(first_name="aliii").update(first_name="ali")
```
- **Note:** The `update()` method updates all matching records in a single query.

### delete

Delete a Single Object with variable
```python
someone = person.objects.get(id=1)
someone.delete()
```

Delete Multiple Objects Using `filter()`
```python
person.objects.filter(first_name="aliii").delete()
```
- **Note:** The `delete()` method deletes all matching records.










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# References