80 lines
2.7 KiB
ReStructuredText
80 lines
2.7 KiB
ReStructuredText
Basic Decorator Operations
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==========================
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Creating a datalite class
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-------------------------
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A datalite class is a special dataclass. It is created by using a decorator ``@datalite.datalite``,
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members of this class are, from Python's perspective, just normal classes. However, they have
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additional methods and attributes. ``@datalite`` decorator needs a database path to be provided.
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This database is the database the table for the dataclass will be created.
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.. code-block:: python
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from datalite import datalite
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@datalite(db_path='db.db')
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@dataclass
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class Student:
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student_id: int = 1
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student_name: str = "Kurt Gödel"
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student_gpa: float = 3.9
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Here, ``datalite`` will create a table called ``student`` in the database file ``db.db``, this
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file will include all the fields of the dataclass as columns. Default value of these columns
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are same as the default value of the dataclass.
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Special Methods
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---------------
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Each object initialised from a dataclass decorated with the ``@dataclass`` decorator automatically
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gains access to three special methods. It should be noted, due to the nature of the library, extensions
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such as ``mypy`` and IDEs such as PyCharm will not be able to see these methods and may raise exceptions.
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With this in mind, let us create a new object and run the methods over this objects.
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.. code-block:: python
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new_student = Student(0, "Albert Einstein", 4.0)
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Creating an Entry
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##################
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First special method is ``.create_entry()`` when called on an object of a class decorated with the
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``@datalite`` decorator, this method creates an entry in the table of the bound database of the class,
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in this case, table named ``student`` in the ``db.db``. Therefore, to create the entry of Albert Einstein
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in the table:
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.. code-block:: python
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new_student.create_entry()
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This also modifies the object in an intresting way, it adds a new attribute ``obj_id``, this is a unique,
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autoincremented value in the database. It can be accessed by ``new_student.obj_id``.
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Updating an Entry
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##################
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Second special method is ``.update_entry()``. If an object's attribute is changed, to update its
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record in the database, this method must be called.
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.. code-block:: python
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new_student.student_gpa = 5.0 # He is Einstein, after all.
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new_student.update_entry()
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Deleting an Entry
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##################
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To delete an entry from the record, the third and last special method, ``.remove_entry()`` should
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be used.
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.. code-block:: python
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new_student.remove_entry()
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.. warning::
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It should be noted that, if the ``new_student.obj_id`` attribute is modified, ``.update_entry()``
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and ``.remove_entry()`` may have unexpected results.
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