Add pagination support

README.md

@@ -11,7 +11,23 @@ using it is extremely simple, say that you have a dataclass definition,
 just add the decorator `@datalite(db_name="db.db")` to the top of the
 definition, and the dataclass will now be bound to the file `db.db`
 
-For example:
+## Download and Install
+
+You can install `datalite` simply by
+
+```shell script
+pip install datalite
+```
+
+Or you can clone the repository and run
+
+```shell script
+python setup.py
+```
+
+Datalite has no dependencies! As it is built on Python 3.7+ standard library. Albeit, its tests require `unittest` library.
+
+## Datalite in Action
 
 ```python
 from dataclasses import dataclass
@@ -30,7 +46,9 @@ table name `student` and rows `student_id`, `student_name` with datatypes
 integer and text, respectively. The default value for `student_name` is
 `John Smith`.
 
-## Entry manipulation
+##Basic Usage
+
+### Entry manipulation
 
 After creating an object traditionally, given that you used the `datalite` decorator,
 the object has three new methods: `.create_entry()`, `.update_entry()`
@@ -81,4 +99,10 @@ The last two helper methods, `fetch_if(class_, condition)` fetches all
 the records of type `class_` that fit a certain condition. Here conditions
 must be written is SQL syntax. For easier, only one conditional checks, there
 is `fetch_equals(class_, field, value)` that checks the value of only one `field`
-and returns the object whose `field` equals the provided `value`.
+and returns the object whose `field` equals the provided `value`.
+
+#### Pagination
+
+`datalite` also supports pagination on `fetch_if`, `fetch_all` and `fetch_where`,
+you can specify `page` number and `element_count` for each page (default 10), for
+these functions in order to get a subgroup of records.

datalite/fetch.py

@@ -3,6 +3,19 @@ from typing import List, Tuple, Any
 from .commons import _convert_sql_format
 
 
+def insert_pagination(query: str, page: int, element_count: int) -> str:
+    """
+    Insert the pagination arguments if page number is given.
+    :param query: Query to insert to
+    :param page: Page to get.
+    :param element_count: Element count in each page.
+    :return: The modified (or not) query.
+    """
+    if page:
+        query += f" ORDER BY obj_id LIMIT {element_count} OFFSET {(page - 1) * element_count}"
+    return query + ";"
+
+
 def is_fetchable(class_: type, obj_id: int) -> bool:
     """
     Check if a record is fetchable given its obj_id and
@@ -83,25 +96,27 @@ def _convert_record_to_object(class_: type, record: Tuple[Any], field_names: Lis
     return obj
 
 
-def fetch_if(class_: type, condition: str) -> tuple:
+def fetch_if(class_: type, condition: str, page: int = 0, element_count: int = 10) -> tuple:
     """
     Fetch all class_ type variables from the bound db,
     provided they fit the given condition
     :param class_: Class type to fetch.
     :param condition: Condition to check for.
+    :param page: Which page to retrieve, default all. (0 means closed).
+    :param element_count: Element count in each page.
     :return: A tuple of records that fit the given condition
     of given type class_.
     """
     table_name = class_.__name__.lower()
     with sql.connect(getattr(class_, 'db_path')) as con:
         cur: sql.Cursor = con.cursor()
-        cur.execute(f"SELECT * FROM {table_name} WHERE {condition};")
+        cur.execute(insert_pagination(f"SELECT * FROM {table_name} WHERE {condition}", page, element_count))
         records: list = cur.fetchall()
         field_names: List[str] = _get_table_cols(cur, table_name)
     return tuple(_convert_record_to_object(class_, record, field_names) for record in records)
 
 
-def fetch_where(class_: type, field: str, value: Any) -> tuple:
+def fetch_where(class_: type, field: str, value: Any, page: int = 0, element_count: int = 10) -> tuple:
     """
     Fetch all class_ type variables from the bound db,
     provided that the field of the records fit the
@@ -109,9 +124,11 @@ def fetch_where(class_: type, field: str, value: Any) -> tuple:
     :param class_: Class of the records.
     :param field: Field to check.
     :param value: Value to check for.
+    :param page: Which page to retrieve, default all. (0 means closed).
+    :param element_count: Element count in each page.
     :return: A tuple of the records.
     """
-    return fetch_if(class_, f"{field} = {_convert_sql_format(value)}")
+    return fetch_if(class_, f"{field} = {_convert_sql_format(value)}", page, element_count)
 
 
 def fetch_range(class_: type, range_: range) -> tuple:
@@ -125,10 +142,12 @@ def fetch_range(class_: type, range_: range) -> tuple:
     return tuple(fetch_from(class_, obj_id) for obj_id in range_ if is_fetchable(class_, obj_id))
 
 
-def fetch_all(class_: type) -> tuple:
+def fetch_all(class_: type, page: int = 0, element_count: int = 10) -> tuple:
     """
     Fetchall the records in the bound database.
     :param class_: Class of the records.
+    :param page: Which page to retrieve, default all. (0 means closed).
+    :param element_count: Element count in each page.
     :return: All the records of type class_ in
     the bound database as a tuple.
     """
@@ -139,7 +158,7 @@ def fetch_all(class_: type) -> tuple:
     with sql.connect(db_path) as con:
         cur: sql.Cursor = con.cursor()
         try:
-            cur.execute(f"SELECT * FROM {class_.__name__.lower()}")
+            cur.execute(insert_pagination(f"SELECT * FROM {class_.__name__.lower()}", page, element_count))
         except sql.OperationalError:
             raise TypeError(f"No record of type {class_.__name__.lower()}")
         records = cur.fetchall()

setup.py

@@ -5,7 +5,7 @@ with open("README.md", "r") as fh:
 
 setuptools.setup(
     name="datalite", # Replace with your own username
-    version="0.5.1",
+    version="0.5.2",
     author="Ege Ozkan",
     author_email="egeemirozkan24@gmail.com",
     description="A small package that binds dataclasses to an sqlite database",

test/main_tests.py

@@ -3,6 +3,7 @@ from datalite import datalite
 from datalite.fetch import fetch_if, fetch_all, fetch_range, fetch_from, fetch_equals, fetch_where
 from sqlite3 import connect
 from dataclasses import dataclass, asdict
+from math import floor
 from os import remove
 
 
@@ -73,7 +74,6 @@ class DatabaseMain(unittest.TestCase):
         self.assertEqual(len(objects), init_len)
 
 
-
 class DatabaseFetchCalls(unittest.TestCase):
     def setUp(self) -> None:
         self.objs = [FetchClass(1, 'a'), FetchClass(2, 'b'), FetchClass(3, 'b')]
@@ -107,5 +107,25 @@ class DatabaseFetchCalls(unittest.TestCase):
         [obj.remove_entry() for obj in self.objs]
 
 
+class DatabaseFetchPaginationCalls(unittest.TestCase):
+    def setUp(self) -> None:
+        self.objs = [FetchClass(i, f'{floor(i/10)}') for i in range(30)]
+        [obj.create_entry() for obj in self.objs]
+
+    def testFetchAllPagination(self):
+        t_objs = fetch_all(FetchClass, 1, 10)
+        self.assertEqual(tuple(self.objs[:10]), t_objs)
+
+    def testFetchWherePagination(self):
+        t_objs = fetch_where(FetchClass, 'str_', '0', 2, 5)
+        self.assertEqual(tuple(self.objs[5:10]), t_objs)
+
+    def testFetchIfPagination(self):
+        t_objs = fetch_if(FetchClass, 'str_ = "0"', 1, 5)
+        self.assertEqual(tuple(self.objs[:5]), t_objs)
+
+    def tearDown(self) -> None:
+        [obj.remove_entry() for obj in self.objs]
+
 if __name__ == '__main__':
     unittest.main()