#50 Implement exists() method

docs/tutorial/models.md

@@ -222,6 +222,14 @@ You can filter data by using the fields of the model.
 users = list(UserModel.objects.filter(username="hakancelik"))
 ```
 
+### Exists
+
+Exists method is used to check if the data exists in the database, returns True if the data exists, otherwise returns False.
+If you pass unique together fields of the model, it will be faster.
+
+```python
+is_exists: bool = UserModel.objects.exists(username="hakancelik")
+``````
 
 ## Model properties
 

src/pydbm/database/manager.py

@@ -193,11 +193,27 @@ def all(self) -> typing.Iterable[DbmModel]:
         for key in self:
             yield self.get(id=key)
 
-    def filter(self, **kwargs) -> typing.Iterable[DbmModel]:
+    def filter(self, **kwargs) -> typing.Iterator[DbmModel]:
         def check(model: DbmModel) -> bool:
             return all(model.fields[key] == value for key, value in kwargs.items())
 
         yield from filter(check, self.all())
 
+    def exists(self, **kwargs) -> bool:
+        if (id := kwargs.pop("id", None)) is None and self.model._config.unique_together == tuple(kwargs.keys()):
+            auto_field = AutoField(
+                field_name=PRIMARY_KEY,
+                field_type=str,
+                unique_together=self.model._config.unique_together
+            )
+            id = auto_field(fields=kwargs).get_default_value()
+
+        if id is not None:
+            with self as db:
+                data_from_dbm: bytes = db.get(id, None)
+            return data_from_dbm is not None
+        else:
+            return not (next(self.filter(**kwargs), False) is False)
+
     def count(self):
         return len(self)

tests/models/test_base.py

@@ -291,3 +291,46 @@ class Model(DbmModel):
 
     Model(username="celik").save()
     assert Model.objects.count() == 2
+
+
+def test_base_exists_true():
+    class Model(DbmModel):
+        username: str
+
+        class Config:
+            unique_together = ("username",)
+
+    Model(username="hakan").save()
+    assert Model.objects.exists(username="hakan") is True
+
+
+def test_base_exists_false():
+    class Model(DbmModel):
+        username: str
+
+    assert Model.objects.exists(username="hakan") is False
+
+
+def test_base_exists_true_more_fields():
+    class Model(DbmModel):
+        username: str
+        name: str
+        surname: str
+
+        class Config:
+            unique_together = ("username",)
+
+    Model(username="hakan", name="hakan", surname="celik").save()
+    assert Model.objects.exists(name="hakan", surname="celik") is True
+
+
+def test_base_exists_false_more_fields():
+    class Model(DbmModel):
+        username: str
+        name: str
+        surname: str
+
+        class Config:
+            unique_together = ("username",)
+
+    assert Model.objects.exists(name="hakan", surname="celik") is False