Add fetch_if, related documention and refactor code slightly.

datalite/__init__.py

@@ -1,6 +1,6 @@
 import sqlite3 as sql
 from dataclasses import Field, asdict, dataclass
-from typing import List, Dict, Optional, Callable, Any
+from typing import List, Dict, Optional, Callable, Any, Tuple
 
 
 def _convert_type(type_: Optional[type], type_overload: Dict[Optional[type], str]) -> str:
@@ -171,6 +171,39 @@ def fetch_from(class_: type, obj_id: int) -> Any:
     return obj
 
 
+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_.
+    :param class_: Class type to convert the record to.
+    :param record: Record to get data from.
+    :param field_names: Field names of the class.
+    :return: the created object.
+    """
+    kwargs = dict(zip(field_names, record[1:]))
+    obj_id = record[0]
+    obj = class_(**kwargs)
+    setattr(obj, "obj_id", obj_id)
+    return obj
+
+
+def fetch_when(class_: type, condition: str) -> 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.
+    :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};")
+        field_names: List[str] = _get_table_cols(cur, table_name)
+        records: list = cur.fetchall()
+    return tuple(_convert_record_to_object(class_, record, field_names) for record in records)
+
+
 def fetch_range(class_: type, range_: range) -> tuple:
     """
     Fetch the records in a given range of object ids.
@@ -182,7 +215,7 @@ 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_if(class_: type) -> tuple:
     """
     Fetchall the records in the bound database.
     :param class_: Class of the records.
@@ -201,11 +234,4 @@ def fetch_all(class_: type) -> tuple:
             raise TypeError(f"No record of type {class_.__name__.lower()}")
         records = cur.fetchall()
         field_names: List[str] = _get_table_cols(cur, class_.__name__.lower())
-    objects: List[class_] = []
-    for record in records:
-        kwargs = dict(zip(field_names, record[1:]))
-        obj_id = record[0]
-        obj = class_(**kwargs)
-        setattr(obj, "obj_id", obj_id)
-        objects.append(obj)
-    return tuple(objects)
+    return tuple(_convert_record_to_object(class_, record, field_names) for record in records)