From a3eed28f425d6c7ac7c08bcea36007cd6135a9a7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ege=20Emir=20=C3=96zkan?= <egeemirozkan24@gmail.com>
Date: Mon, 10 Aug 2020 05:39:56 +0300
Subject: [PATCH] Reverted fetch_from, added fetch_equals for better
 documentation and simplicity.

---
 README.md            | 15 ++++++++-------
 datalite/__init__.py | 15 ++++++++++++++-
 test/main_tests.py   |  6 +++---
 3 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/README.md b/README.md
index 3fcee99..92196a2 100644
--- a/README.md
+++ b/README.md
@@ -62,22 +62,23 @@ inserted onto the system.
 > :warning: **Limitation! Fetch can only fetch limited classes correctly**: int, float and str!
 
 Finally, you may wish to recreate objects from a table that already exist, for
-this purpose we have the function `fetch_from(class_, value, field)` as well
+this purpose we have the function `fetch_from(class_, obj_id)` as well
 as `is_fetchable(className, object_id)` former fetches a record from the
-SQL database given a field and value. If only the value is provided,
- field defaults to 'obj_id' which is unique for all objects,
- whereas the latter checks if it is fetchable (most likely to check if it exists.)
+SQL database given its unique object_id  whereas the latter checks if it 
+is fetchable (most likely to check if it exists.)
 
 ```python
 >>> fetch_from(Student, 2)
 Student(student_id=10, student_name='Albert Einstein')
 ```
 
-We have three helper methods, `fetch_range(class_, range_)` and
+We have four helper methods, `fetch_range(class_, range_)` and
 `fetch_all(class_)` are very similar: the former fetches the records
 fetchable from the object id range provided by the user, whereas the
 latter fetches all records. Both return a tuple of `class_` objects.
 
-The last helper method, `fetch_if(class_, condition)` fetches all
+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. Be careful about the string espacially.
\ No newline at end of file
+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`.
\ No newline at end of file
diff --git a/datalite/__init__.py b/datalite/__init__.py
index fc72f89..d8fd205 100644
--- a/datalite/__init__.py
+++ b/datalite/__init__.py
@@ -171,7 +171,7 @@ def _get_table_cols(cur: sql.Cursor, table_name: str) -> List[str]:
     return [row_info[1] for row_info in cur.fetchall()][1:]
 
 
-def fetch_from(class_: type, value: Any, field: str = 'obj_id') -> Any:
+def fetch_equals(class_: type, field: str, value: Any, ) -> Any:
     """
     Fetch a class_ type variable from its bound db.
     :param class_: Class to fetch.
@@ -191,6 +191,19 @@ def fetch_from(class_: type, value: Any, field: str = 'obj_id') -> Any:
     return obj
 
 
+def fetch_from(class_: type, obj_id: int) -> Any:
+    """
+    Fetch a class_ type variable from its bound dv.
+    :param class_: Class to fetch from.
+    :param obj_id: Unique object id of the object.
+    :return: The fetched object.
+    """
+    if not is_fetchable(class_, obj_id):
+        raise KeyError(f"An object with {obj_id} of type {class_.__name__} does not exist, or"
+                       f"otherwise is unreachable.")
+    return fetch_equals(class_, 'obj_id', obj_id)
+
+
 def _convert_record_to_object(class_: type, record: Tuple[Any], field_names: List[str]) -> Any:
     """
     Convert a given record fetched from an SQL instance to a Python Object of given class_.
diff --git a/test/main_tests.py b/test/main_tests.py
index 75c478b..97a0a32 100644
--- a/test/main_tests.py
+++ b/test/main_tests.py
@@ -1,5 +1,5 @@
 import unittest
-from datalite import datalite, fetch_if, fetch_all, fetch_range, fetch_from
+from datalite import datalite, fetch_if, fetch_all, fetch_range, fetch_from, fetch_equals
 from sqlite3 import connect
 from dataclasses import dataclass, asdict
 from os import remove
@@ -82,8 +82,8 @@ class DatabaseFetchCalls(unittest.TestCase):
         t_obj = fetch_from(FetchClass, self.objs[0].obj_id)
         self.assertEqual(self.objs[0], t_obj)
 
-    def testFetchFromDif(self):
-        t_obj = fetch_from(FetchClass, self.objs[0].str_, 'str_')
+    def testFetchEquals(self):
+        t_obj = fetch_equals(FetchClass, 'str_', self.objs[0].str_)
         self.assertEqual(self.objs[0], t_obj)
 
     def testFetchAll(self):