{"id":75310,"date":"2020-01-18T14:17:47","date_gmt":"2020-01-18T08:47:47","guid":{"rendered":"https:\/\/www.vskills.in\/certification\/tutorial\/?p=75310"},"modified":"2024-04-12T14:17:13","modified_gmt":"2024-04-12T08:47:13","slug":"installing-the-model","status":"publish","type":"page","link":"https:\/\/www.vskills.in\/certification\/tutorial\/installing-the-model\/","title":{"rendered":"Installing the Model"},"content":{"rendered":"

We\u2019ve written the code; now let\u2019s create the tables in our database. In order to do that, the first step is to activate<\/em> these models in our Django project. We do that by adding the books app to the list of installed apps in the settings file. Edit the settings.py file again, and look for the INSTALLED_APPS setting. INSTALLED_APPS tells Django which apps are activated for a given project. By default, it looks something like this:<\/p>\n

INSTALLED_APPS = [\n'django.contrib.admin',\n'django.contrib.auth',\n'django.contrib.contenttypes',\n'django.contrib.sessions',\n'django.contrib.messages',\n'django.contrib.staticfiles',\n]<\/pre>\n
To register our \u201cbooks\u201d app, add ‘books.apps.BooksConfig’ to INSTALLED_APPS, so the setting ends up looking like this:<\/span><\/p>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/span>INSTALLED_APPS = [\n<\/span>'books.apps.BooksConfig',\n<\/span>'django.contrib.admin',\n<\/span>'django.contrib.auth',\n<\/span>'django.contrib.contenttypes',\n<\/span>'django.contrib.sessions',\n<\/span>'django.contrib.messages',\n<\/span>'django.contrib.staticfiles',\n<\/span>]<\/span><\/pre>\n
Each app in INSTALLED_APPS is represented by its full Python path \u2013 that is, the path of packages, separated by dots, leading to the app package. The dotted path in this case points to the BooksConfig class that Django created for you in the apps.py file. Well will look at app configurations in more detail later in the book.<\/p>\n
Now that the Django app has been activated in the settings file, we can create the database tables in our database. First, let\u2019s validate the models by running this command:<\/p>\n
python manage.py check<\/pre>\n
The check command runs the Django system check framework \u2013 a set of static checks for validating Django projects. If all is well, you\u2019ll see the message System check identified no issues (0 silenced). If you don\u2019t, make sure you typed in the model code correctly. The error output should give you helpful information about what was wrong with the code. Any time you think you have problems with your models, run python manage.py check. It tends to catch all the common model problems.<\/p>\n
If your models are valid, run the following command to tell Django that you have made some changes to your models (in this case, you have made a new one):<\/p>\n
\u00a0 python manage.py makemigrations books<\/pre>\n
You should see something similar to the following:<\/p>\n
Migrations for 'books':\n0001_initial.py:\n- Create model Author\n- Create model Book\n- Create model Publisher\n- Add field publisher to book<\/pre>\n
Migrations are how Django stores changes to your models (and thus your database schema) \u2013 they\u2019re just files on disk. In this instance, you will find a file names 0001_initial.py in the \\migrations folder of the books app. The migrate command will take your latest migration file and update your database schema automatically, but first, let\u2019s see what SQL that migration would run. The sqlmigrate command takes migration names and returns their SQL:<\/p>\n
python manage.py sqlmigrate books 0001<\/pre>\n
You should see something similar to the following (reformatted for readability):<\/p>\n
BEGIN;<\/pre>\n
CREATE TABLE \"books_author\" (\n\"id\" integer NOT NULL PRIMARY KEY AUTOINCREMENT,\n\"first_name\" varchar(30) NOT NULL,\n\"last_name\" varchar(40) NOT NULL,\n\"email\" varchar(254) NOT NULL\n);\nCREATE TABLE \"books_book\" (\n\"id\" integer NOT NULL PRIMARY KEY AUTOINCREMENT,\n\"title\" varchar(100) NOT NULL,\n\"publication_date\" date NOT NULL\n);\nCREATE TABLE \"books_book_authors\" (\n\"id\" integer NOT NULL PRIMARY KEY AUTOINCREMENT,\n\"book_id\" integer NOT NULL REFERENCES \"books_book\" (\"id\"),\n\"author_id\" integer NOT NULL REFERENCES \"books_author\" (\"id\"),\nUNIQUE (\"book_id\", \"author_id\")\n);\nCREATE TABLE \"books_publisher\" (\n\"id\" integer NOT NULL PRIMARY KEY AUTOINCREMENT,\n\"name\" varchar(30) NOT NULL,\n\"address\" varchar(50) NOT NULL,\n\"city\" varchar(60) NOT NULL,\n\"state_province\" varchar(30) NOT NULL,\n\"country\" varchar(50) NOT NULL,\n\"website\" varchar(200) NOT NULL\n);\nCREATE TABLE \"books_book__new\" (\n\"id\" integer NOT NULL PRIMARY KEY AUTOINCREMENT,\n\"title\" varchar(100) NOT NULL,\n\"publication_date\" date NOT NULL,\n\"publisher_id\" integer NOT NULL REFERENCES\n\"books_publisher\" (\"id\")\n);\n\nINSERT INTO \"books_book__new\" (\"id\", \"publisher_id\", \"title\",\n\"publication_date\") SELECT \"id\", NULL, \"title\", \"publication_date\" FROM\n\"books_book\";\n\nDROP TABLE \"books_book\";\n\nALTER TABLE \"books_book__new\" RENAME TO \"books_book\";\n\nCREATE INDEX \"books_book_2604cbea\" ON \"books_book\" (\"publisher_id\");\n\nCOMMIT;\n\n<\/pre>\n
Note the following:<\/span><\/p>\n