server: when updating post tags, trim metrics related to removed tags (via FK)

6 files changed, 211 insertions, 107 deletions

diff --git a/server/szurubooru/func/metrics.py b/server/szurubooru/func/metrics.py
index ab5a0c4..80ea073 100644
--- a/server/szurubooru/func/metrics.py
+++ b/server/szurubooru/func/metrics.py
@@ -237,7 +237,7 @@ def update_or_create_post_metric_ranges(
     Overwrites any existing post metrics, deletes other existing post metrics.
     """
     assert post
-    post.metrics = []
+    post.metric_ranges = []
     for metric_data in metric_ranges_data:
         for field in ('tag_name', 'low', 'high'):
             if field not in metric_data:
diff --git a/server/szurubooru/migrations/versions/0061c5c3299f_postmetric_depends_on_posttag.py b/server/szurubooru/migrations/versions/0061c5c3299f_postmetric_depends_on_posttag.py
new file mode 100644
index 0000000..be8fc08
--- /dev/null
+++ b/server/szurubooru/migrations/versions/0061c5c3299f_postmetric_depends_on_posttag.py
@@ -0,0 +1,35 @@
+'''
+PostMetric depends on PostTag
+
+Revision ID: 0061c5c3299f
+Created at: 2019-04-20 14:02:23.229492
+'''
+
+import sqlalchemy as sa
+from alembic import op
+
+
+revision = '0061c5c3299f'
+down_revision = 'aae2050fb28c'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.create_foreign_key(
+        'post_metric_post_tag_fkey', 'post_metric', 'post_tag',
+        ['post_id', 'tag_id'], ['post_id', 'tag_id'],
+        ondelete='cascade')
+    op.create_foreign_key(
+        'post_metric_range_post_tag_fkey', 'post_metric_range', 'post_tag',
+        ['post_id', 'tag_id'], ['post_id', 'tag_id'],
+        ondelete='cascade')
+
+
+def downgrade():
+    op.drop_constraint(
+        'post_metric_post_tag_fkey', 'post_metric',
+        type_='foreignKey')
+    op.drop_constraint(
+        'post_metric_range_post_tag_fkey', 'post_metric',
+        type_='foreignKey')
diff --git a/server/szurubooru/model/metric.py b/server/szurubooru/model/metric.py
index c3b5f11..530165a 100644
--- a/server/szurubooru/model/metric.py
+++ b/server/szurubooru/model/metric.py
@@ -1,5 +1,6 @@
 import sqlalchemy as sa
 from szurubooru.model.base import Base
+from szurubooru.model.post import PostTag
 from szurubooru.model.tag import TagName
 
 
@@ -26,9 +27,18 @@ class PostMetric(Base):
     post = sa.orm.relationship('Post')
     metric = sa.orm.relationship('Metric', back_populates='post_metrics')
 
+    __table_args__ = (sa.ForeignKeyConstraint(
+        (post_id, tag_id),
+        (PostTag.post_id, PostTag.tag_id),
+        ondelete='cascade'),
+    )
     __mapper_args__ = {
         'version_id_col': version,
         'version_id_generator': False,
+        # when deleting tag or post, cascade will ensure this post metric is
+        # also deleted, but sqlalchemy will try to delete it twice because of
+        # the cascade on foreign key into PostTag. This silences the error:
+        'confirm_deleted_rows': False,
     }
 
 
@@ -60,9 +70,18 @@ class PostMetricRange(Base):
     post = sa.orm.relationship('Post')
     metric = sa.orm.relationship('Metric', back_populates='post_metric_ranges')
 
+    __table_args__ = (sa.ForeignKeyConstraint(
+        (post_id, tag_id),
+        (PostTag.post_id, PostTag.tag_id),
+        ondelete='cascade'),
+    )
     __mapper_args__ = {
         'version_id_col': version,
         'version_id_generator': False,
+        # when deleting tag or post, cascade will ensure this post metric is
+        # also deleted, but sqlalchemy will try to delete it twice because of
+        # the cascade on foreign key into PostTag. This silences the error:
+        'confirm_deleted_rows': False,
     }
 
 
@@ -92,18 +111,18 @@ class Metric(Base):
     tag_name = sa.orm.column_property(
         (
             sa.sql.expression.select([TagName.name])
-            .where(TagName.tag_id == tag_id)
-            .order_by(TagName.order)
-            .limit(1)
-            .as_scalar()
+                .where(TagName.tag_id == tag_id)
+                .order_by(TagName.order)
+                .limit(1)
+                .as_scalar()
         ))
 
     post_metric_count = sa.orm.column_property(
         (
             sa.sql.expression.select(
                 [sa.sql.expression.func.count(PostMetric.post_id)])
-            .where(PostMetric.tag_id == tag_id)
-            .correlate_except(PostMetric)
+                .where(PostMetric.tag_id == tag_id)
+                .correlate_except(PostMetric)
         ),
         deferred=True)
 
@@ -111,8 +130,8 @@ class Metric(Base):
         (
             sa.sql.expression.select(
                 [sa.sql.expression.func.count(PostMetricRange.post_id)])
-            .where(PostMetricRange.tag_id == tag_id)
-            .correlate_except(PostMetricRange)
+                .where(PostMetricRange.tag_id == tag_id)
+                .correlate_except(PostMetricRange)
         ),
         deferred=True)
 
diff --git a/server/szurubooru/tests/conftest.py b/server/szurubooru/tests/conftest.py
index 084e6e5..c61e7c3 100644
--- a/server/szurubooru/tests/conftest.py
+++ b/server/szurubooru/tests/conftest.py
@@ -32,11 +32,18 @@ class QueryCounter:
         return self._statements
 
 
+def _set_sqlite_pragma(dbapi_connection, connection_record):
+    cursor = dbapi_connection.cursor()
+    cursor.execute('PRAGMA foreign_keys=ON')
+    cursor.close()
+
+
 if not config.config['test_database']:
     raise RuntimeError('Test database not configured.')
 
 _query_counter = QueryCounter()
 _engine = sa.create_engine(config.config['test_database'])
+sa.event.listen(_engine, 'connect', _set_sqlite_pragma)
 model.Base.metadata.drop_all(bind=_engine)
 model.Base.metadata.create_all(bind=_engine)
 sa.event.listen(
@@ -198,7 +205,8 @@ def post_factory(skip_post_hashing):
             id=None,
             safety=model.Post.SAFETY_SAFE,
             type=model.Post.TYPE_IMAGE,
-            checksum='...'):
+            checksum='...',
+            tags=[]):
         post = model.Post()
         post.post_id = id
         post.safety = safety
@@ -207,6 +215,7 @@ def post_factory(skip_post_hashing):
         post.flags = []
         post.mime_type = 'application/octet-stream'
         post.creation_time = datetime(1996, 1, 1)
+        post.tags = tags
         return post
     return factory
 
diff --git a/server/szurubooru/tests/func/test_metrics.py b/server/szurubooru/tests/func/test_metrics.py
index 0db76c4..d8d0cbd 100644
--- a/server/szurubooru/tests/func/test_metrics.py
+++ b/server/szurubooru/tests/func/test_metrics.py
@@ -42,26 +42,26 @@ def test_serialize_post_metric_range(tag_factory, metric_factory):
 
 def test_try_get_post_metric(
         post_factory, metric_factory, post_metric_factory):
-    post = post_factory()
-    metric = metric_factory()
+    metric1 = metric_factory()
     metric2 = metric_factory()
-    post_metric = post_metric_factory(post=post, metric=metric)
-    db.session.add_all([post, metric, metric2, post_metric])
+    post = post_factory(tags=[metric1.tag, metric2.tag])
+    post_metric = post_metric_factory(post=post, metric=metric1)
+    db.session.add_all([post, metric1, metric2, post_metric])
     db.session.flush()
     assert metrics.try_get_post_metric(post, metric2) is None
-    assert metrics.try_get_post_metric(post, metric) is post_metric
+    assert metrics.try_get_post_metric(post, metric1) is post_metric
 
 
 def test_try_get_post_metric_range(
         post_factory, metric_factory, post_metric_range_factory):
-    post = post_factory()
-    metric = metric_factory()
+    metric1 = metric_factory()
     metric2 = metric_factory()
-    post_metric_range = post_metric_range_factory(post=post, metric=metric)
-    db.session.add_all([post, metric, metric2, post_metric_range])
+    post = post_factory(tags=[metric1.tag, metric2.tag])
+    post_metric_range = post_metric_range_factory(post=post, metric=metric1)
+    db.session.add_all([post, metric1, metric2, post_metric_range])
     db.session.flush()
     assert metrics.try_get_post_metric_range(post, metric2) is None
-    assert metrics.try_get_post_metric_range(post, metric) is post_metric_range
+    assert metrics.try_get_post_metric_range(post, metric1) is post_metric_range
 
 
 def test_get_all_metrics(metric_factory):
@@ -137,33 +137,25 @@ def test_update_or_create_post_metric_without_tag(post_factory, metric_factory):
 
 
 def test_update_or_create_post_metric_with_value_out_of_range(
-        post_factory, tag_factory, metric_factory):
-    post = post_factory()
-    tag = tag_factory()
-    post.tags = [tag]
-    metric = metric_factory(tag)
+        post_factory, metric_factory):
+    metric = metric_factory()
+    post = post_factory(tags=[metric.tag])
     with pytest.raises(metrics.MetricValueOutOfRangeError):
         metrics.update_or_create_post_metric(post, metric, -99)
 
 
-def test_update_or_create_post_metric_create(
-        post_factory, tag_factory, metric_factory):
-    post = post_factory()
-    tag = tag_factory()
-    post.tags = [tag]
-    metric = metric_factory(tag)
+def test_update_or_create_post_metric_create(post_factory, metric_factory):
+    metric = metric_factory()
+    post = post_factory(tags=[metric.tag])
     db.session.add(metric)
     db.session.flush()
     post_metric = metrics.update_or_create_post_metric(post, metric, 1.5)
     assert post_metric.value == 1.5
 
 
-def test_update_or_create_post_metric_update(
-        post_factory, tag_factory, metric_factory):
-    post = post_factory()
-    tag = tag_factory()
-    post.tags = [tag]
-    metric = metric_factory(tag)
+def test_update_or_create_post_metric_update(post_factory, metric_factory):
+    metric = metric_factory()
+    post = post_factory(tags=[metric.tag])
     post_metric = model.PostMetric(post=post, metric=metric, value=1.2)
     db.session.add(post_metric)
     db.session.flush()
@@ -200,9 +192,8 @@ def test_update_or_create_post_metrics_with_missing_fields(
 
 def test_update_or_create_post_metrics_with_invalid_tag(
         post_factory, tag_factory):
-    post = post_factory()
     tag = tag_factory(names=['tag1'])
-    post.tags = [tag]
+    post = post_factory(tags=[tag])
     db.session.add(tag)
     db.session.flush()
     data = [{'tag_name': 'tag1', 'value': 2}]
@@ -212,10 +203,9 @@ def test_update_or_create_post_metrics_with_invalid_tag(
 
 def test_update_or_create_post_metrics(
         post_factory, tag_factory, metric_factory):
-    post = post_factory()
     tag1 = tag_factory(names=['tag1'])
     tag2 = tag_factory(names=['tag2'])
-    post.tags = [tag1, tag2]
+    post = post_factory(tags=[tag1, tag2])
     metric1 = metric_factory(tag1)
     metric2 = metric_factory(tag2)
     db.session.add_all([metric1, metric2])
@@ -233,6 +223,31 @@ def test_update_or_create_post_metrics(
     assert post.metrics[1].value == 3.4
 
 
+def test_update_or_create_post_metrics_with_trim(
+        post_factory, tag_factory, metric_factory, post_metric_factory):
+    tag1 = tag_factory(names=['tag1'])
+    tag2 = tag_factory(names=['tag2'])
+    post = post_factory(tags=[tag1, tag2])
+    metric1 = metric_factory(tag1)
+    metric2 = metric_factory(tag2)
+    post_metric = post_metric_factory(post=post, metric=metric1, value=1.2)
+    db.session.add_all([post, tag1, tag2, metric1, metric2, post_metric])
+    db.session.flush()
+    assert len(post.metrics) == 1
+    assert post.metrics[0].metric == metric1
+    assert post.metrics[0].value == 1.2
+
+    data = [
+        {'tag_name': 'tag2', 'value': 3.4},
+    ]
+    metrics.update_or_create_post_metrics(post, data)
+    db.session.flush()
+
+    assert len(post.metrics) == 1
+    assert post.metrics[0].metric == metric2
+    assert post.metrics[0].value == 3.4
+
+
 # Post metric ranges
 
 def test_update_or_create_post_metric_range_without_tag(
@@ -247,21 +262,17 @@ def test_update_or_create_post_metric_range_without_tag(
     (-99, 1), (1, 99),
 ])
 def test_update_or_create_post_metric_range_with_values_out_of_range(
-        low, high, post_factory, tag_factory, metric_factory):
-    post = post_factory()
-    tag = tag_factory()
-    post.tags = [tag]
-    metric = metric_factory(tag)
+        low, high, post_factory, metric_factory):
+    metric = metric_factory()
+    post = post_factory(tags=[metric.tag])
     with pytest.raises(metrics.MetricValueOutOfRangeError):
         metrics.update_or_create_post_metric_range(post, metric, low, high)
 
 
 def test_update_or_create_post_metric_range_create(
-        post_factory, tag_factory, metric_factory):
-    post = post_factory()
-    tag = tag_factory()
-    post.tags = [tag]
-    metric = metric_factory(tag)
+        post_factory, metric_factory):
+    metric = metric_factory()
+    post = post_factory(tags=[metric.tag])
     db.session.add(metric)
     db.session.flush()
     post_metric_range = metrics.update_or_create_post_metric_range(
@@ -271,11 +282,9 @@ def test_update_or_create_post_metric_range_create(
 
 
 def test_update_or_create_post_metric_range_update(
-        post_factory, tag_factory, metric_factory):
-    post = post_factory()
-    tag = tag_factory()
-    post.tags = [tag]
-    metric = metric_factory(tag)
+        post_factory, metric_factory):
+    metric = metric_factory()
+    post = post_factory(tags=[metric.tag])
     post_metric_range = model.PostMetricRange(
         post=post, metric=metric, low=2, high=3)
     db.session.add(post_metric_range)
@@ -308,18 +317,16 @@ def test_update_or_create_post_metric_ranges_missing_tag(
 ])
 def test_update_or_create_post_metric_ranges_with_missing_fields(
         params, post_factory, tag_factory):
-    post = post_factory()
     tag = tag_factory(names=['tag'])
-    post.tags = [tag]
+    post = post_factory(tags=[tag])
     with pytest.raises(metrics.InvalidMetricError):
         metrics.update_or_create_post_metric_ranges(post, params)
 
 
 def test_update_or_create_post_metric_ranges_with_invalid_tag(
         post_factory, tag_factory):
-    post = post_factory()
     tag = tag_factory(names=['tag1'])
-    post.tags = [tag]
+    post = post_factory(tags=[tag])
     db.session.add(tag)
     db.session.flush()
     data = [{'tag_name': 'tag1', 'low': 2, 'high': 3}]
@@ -329,9 +336,8 @@ def test_update_or_create_post_metric_ranges_with_invalid_tag(
 
 def test_update_or_create_post_metric_ranges_with_invalid_values(
         post_factory, tag_factory, metric_factory):
-    post = post_factory()
     tag = tag_factory(names=['tag1'])
-    post.tags = [tag]
+    post = post_factory(tags=[tag])
     metric = metric_factory(tag=tag)
     db.session.add_all([metric, tag])
     db.session.flush()
@@ -344,10 +350,9 @@ def test_update_or_create_post_metric_ranges_with_invalid_values(
 
 def test_update_or_create_post_metric_ranges(
         post_factory, tag_factory, metric_factory):
-    post = post_factory()
     tag1 = tag_factory(names=['tag1'])
     tag2 = tag_factory(names=['tag2'])
-    post.tags = [tag1, tag2]
+    post = post_factory(tags=[tag1, tag2])
     metric1 = metric_factory(tag1)
     metric2 = metric_factory(tag2)
     db.session.add_all([metric1, metric2])
@@ -365,3 +370,31 @@ def test_update_or_create_post_metric_ranges(
     assert post.metric_ranges[0].high == 3
     assert post.metric_ranges[1].low == 4
     assert post.metric_ranges[1].high == 5
+
+
+def test_update_or_create_post_metric_ranges_with_trim(
+        post_factory, tag_factory, metric_factory, post_metric_range_factory):
+    tag1 = tag_factory(names=['tag1'])
+    tag2 = tag_factory(names=['tag2'])
+    post = post_factory(tags=[tag1, tag2])
+    metric1 = metric_factory(tag1)
+    metric2 = metric_factory(tag2)
+    post_metric_range = post_metric_range_factory(
+        post=post, metric=metric1, low=1, high=2)
+    db.session.add_all([post, tag1, tag2, metric1, metric2, post_metric_range])
+    db.session.flush()
+    assert len(post.metric_ranges) == 1
+    assert post.metric_ranges[0].metric == metric1
+    assert post.metric_ranges[0].low == 1
+    assert post.metric_ranges[0].high == 2
+
+    data = [
+        {'tag_name': 'tag2', 'low': 3, 'high': 4},
+    ]
+    metrics.update_or_create_post_metric_ranges(post, data)
+    db.session.flush()
+
+    assert len(post.metric_ranges) == 1
+    assert post.metric_ranges[0].metric == metric2
+    assert post.metric_ranges[0].low == 3
+    assert post.metric_ranges[0].high == 4
diff --git a/server/szurubooru/tests/model/test_metric.py b/server/szurubooru/tests/model/test_metric.py
index 2b0a13a..69d7bfa 100644
--- a/server/szurubooru/tests/model/test_metric.py
+++ b/server/szurubooru/tests/model/test_metric.py
@@ -2,11 +2,12 @@ from szurubooru import db, model
 
 
 def test_saving_metric(post_factory, tag_factory):
-    post = post_factory()
     tag = tag_factory()
+    post = post_factory(tags=[tag])
     metric = model.Metric(tag=tag, min=1., max=10.)
     post_metric = model.PostMetric(metric=metric, post=post, value=5.5)
-    post_metric_range = model.PostMetricRange(metric=metric, post=post, low=2., high=8.)
+    post_metric_range = model.PostMetricRange(metric=metric, post=post,
+                                              low=2., high=8.)
     db.session.add_all([post, tag, metric, post_metric, post_metric_range])
     db.session.commit()
 
@@ -53,9 +54,9 @@ def test_saving_metric(post_factory, tag_factory):
 
 
 def test_cascade_delete_metric(post_factory, tag_factory):
-    post1 = post_factory()
-    post2 = post_factory()
     tag = tag_factory()
+    post1 = post_factory(tags=[tag])
+    post2 = post_factory(tags=[tag])
     metric = model.Metric(tag=tag, min=1., max=10.)
     post_metric1 = model.PostMetric(metric=metric, post=post1, value=2.3)
     post_metric2 = model.PostMetric(metric=metric, post=post2, value=4.5)
@@ -84,9 +85,9 @@ def test_cascade_delete_metric(post_factory, tag_factory):
 
 
 def test_cascade_delete_tag(post_factory, tag_factory):
-    post = post_factory()
     tag1 = tag_factory()
     tag2 = tag_factory()
+    post = post_factory(tags=[tag1, tag2])
     metric1 = model.Metric(tag=tag1, min=1., max=10.)
     metric2 = model.Metric(tag=tag2, min=2., max=20.)
     post_metric1 = model.PostMetric(metric=metric1, post=post, value=2.3)
@@ -97,7 +98,7 @@ def test_cascade_delete_tag(post_factory, tag_factory):
         metric=metric2, post=post, low=2, high=8)
     db.session.add_all([post, tag1, tag2, metric1, metric2, post_metric1,
                         post_metric2, post_metric_range1, post_metric_range2])
-    db.session.flush()
+    db.session.commit()
 
     assert not db.session.dirty
     assert db.session.query(model.Post).count() == 1
@@ -118,9 +119,9 @@ def test_cascade_delete_tag(post_factory, tag_factory):
 
 
 def test_cascade_delete_post(post_factory, tag_factory):
-    post1 = post_factory()
-    post2 = post_factory()
     tag = tag_factory()
+    post1 = post_factory(tags=[tag])
+    post2 = post_factory(tags=[tag])
     metric = model.Metric(tag=tag, min=1., max=10.)
     post_metric1 = model.PostMetric(metric=metric, post=post1, value=2.3)
     post_metric2 = model.PostMetric(metric=metric, post=post2, value=4.5)
@@ -130,7 +131,7 @@ def test_cascade_delete_post(post_factory, tag_factory):
         metric=metric, post=post2, low=2, high=8)
     db.session.add_all([post1, post2, tag, metric, post_metric1, post_metric2,
                         post_metric_range1, post_metric_range2])
-    db.session.flush()
+    db.session.commit()
 
     assert not db.session.dirty
     assert db.session.query(model.Post).count() == 2
@@ -151,11 +152,14 @@ def test_cascade_delete_post(post_factory, tag_factory):
 
 
 def test_delete_post_metric_no_cascade(
-        metric_factory, post_metric_factory, post_metric_range_factory):
-    metric = metric_factory()
-    post_metric = post_metric_factory(metric=metric)
-    post_metric_range = post_metric_range_factory(metric=metric)
-    db.session.add_all([metric, post_metric, post_metric_range])
+        post_factory, tag_factory, metric_factory,
+        post_metric_factory, post_metric_range_factory):
+    tag = tag_factory()
+    post = post_factory(tags=[tag])
+    metric = metric_factory(tag=tag)
+    post_metric = post_metric_factory(post=post, metric=metric)
+    post_metric_range = post_metric_range_factory(post=post, metric=metric)
+    db.session.add(metric)
     db.session.commit()
     assert len(metric.post_metrics) == 1
 
@@ -166,33 +170,6 @@ def test_delete_post_metric_no_cascade(
     assert len(metric.post_metric_ranges) == 0
 
 
-def test_cascade_delete_on_remove_metric_from_post(
-        post_factory, post_metric_factory, post_metric_range_factory):
-    post = post_factory()
-    post_metric = post_metric_factory(post=post)
-    post_metric_range = post_metric_range_factory(post=post)
-    db.session.add_all([post, post_metric, post_metric_range])
-    db.session.commit()
-
-    assert not db.session.dirty
-    assert db.session.query(model.Post).count() == 1
-    assert db.session.query(model.Tag).count() == 2
-    assert db.session.query(model.Metric).count() == 2
-    assert db.session.query(model.PostMetric).count() == 1
-    assert db.session.query(model.PostMetricRange).count() == 1
-
-    post.metrics.clear()
-    post.metric_ranges.clear()
-    db.session.commit()
-
-    assert not db.session.dirty
-    assert db.session.query(model.Post).count() == 1
-    assert db.session.query(model.Tag).count() == 2
-    assert db.session.query(model.Metric).count() == 2
-    assert db.session.query(model.PostMetric).count() == 0
-    assert db.session.query(model.PostMetricRange).count() == 0
-
-
 def test_tag_without_metric(tag_factory):
     tag = tag_factory(names=['mytag'])
     assert tag.metric is None
@@ -208,9 +185,9 @@ def test_tag_without_metric(tag_factory):
 
 
 def test_metric_counts(post_factory, metric_factory):
-    post1 = post_factory()
-    post2 = post_factory()
     metric = metric_factory()
+    post1 = post_factory(tags=[metric.tag])
+    post2 = post_factory(tags=[metric.tag])
     post_metric1 = model.PostMetric(post=post1, metric=metric, value=1.2)
     post_metric2 = model.PostMetric(post=post2, metric=metric, value=3.4)
     post_metric_range = model.PostMetricRange(post=post1, metric=metric, low=5.6, high=7.8)
@@ -218,3 +195,34 @@ def test_metric_counts(post_factory, metric_factory):
     db.session.flush()
     assert metric.post_metric_count == 2
     assert metric.post_metric_range_count == 1
+
+
+def test_cascade_on_remove_tag_from_post(
+        post_factory, tag_factory, metric_factory,
+        post_metric_factory, post_metric_range_factory):
+    tag = tag_factory()
+    post = post_factory(tags=[tag])
+    metric = metric_factory(tag=tag)
+    post_metric = post_metric_factory(post=post, metric=metric)
+    post_metric_range = post_metric_range_factory(post=post, metric=metric)
+    db.session.add_all([post, tag, metric, post_metric, post_metric_range])
+    db.session.commit()
+
+    assert not db.session.dirty
+    assert db.session.query(model.Post).count() == 1
+    assert db.session.query(model.Tag).count() == 1
+    assert db.session.query(model.PostTag).count() == 1
+    assert db.session.query(model.Metric).count() == 1
+    assert db.session.query(model.PostMetric).count() == 1
+    assert db.session.query(model.PostMetricRange).count() == 1
+
+    post.tags.clear()
+    db.session.commit()
+
+    assert not db.session.dirty
+    assert db.session.query(model.Post).count() == 1
+    assert db.session.query(model.Tag).count() == 1
+    assert db.session.query(model.PostTag).count() == 0
+    assert db.session.query(model.Metric).count() == 1
+    assert db.session.query(model.PostMetric).count() == 0
+    assert db.session.query(model.PostMetricRange).count() == 0