Resolve "Expand the `create_damage_view` function with an overwrite option"

Implement the overwrite option when creating a damage view.

Closes #26 (closed)

\approve @tara @shinde @laurens

exposurelib/database.py

@@ -251,7 +251,9 @@ class ExposureDatabase(SpatialiteDatabase):
         self.connection.execute(sql_statement)
         logger.debug("Table DamageMethod created")
 
-    def create_damage_view(self, view_name, entity, method_id, damage_state_id=None):
+    def create_damage_view(
+        self, view_name, entity, method_id, damage_state_id=None, overwrite=True
+    ):
         """
         Creates a view of damage assessments with the geometry from the respective entity.
         The `method_id` selects the assessments to be selected. If `damage_state_id` is given,
@@ -278,15 +280,27 @@ class ExposureDatabase(SpatialiteDatabase):
                 damage assessment to be displayed. `None` only works for `building` entities,
                 because deterministic damage assessment can only be provided for `building`s
                 and by sources other than the loss-calculator.
+            overwrite (bool):
+                If set, an potentially existing view of the same name is removed first.
         """
 
         # Check for viable parameter combination
         if (damage_state_id is None) and (entity != "building"):
             raise ValueError("Invalid parameter combination for damage view")
 
+        # View names must be in lower case (SQLite requirement)
+        name = view_name.lower()
+
+        # If view already exists, overwrite or raise an exception if overwrite set to False
+        if self.view_exists(name):
+            if not overwrite:
+                raise Exception("View %s already exists" % name)
+            else:
+                self.delete_view(name)
+
         # Create view
         if (entity == "building") or (entity == "residual"):
-            sql_statement = "CREATE VIEW %s AS " % view_name.lower()
+            sql_statement = "CREATE VIEW %s AS " % name
             sql_statement += "SELECT DamageAssessment.id AS idx, Entity.geom AS geometry, "
             sql_statement += "Entity.quadkey, "
             if damage_state_id is None:
@@ -305,7 +319,7 @@ class ExposureDatabase(SpatialiteDatabase):
             if damage_state_id is not None:
                 sql_statement += "AND Damage.damage_state_id = %d " % damage_state_id
         else:  # entity == "tile"
-            sql_statement = "CREATE VIEW %s AS " % view_name.lower()
+            sql_statement = "CREATE VIEW %s AS " % name
             sql_statement += "SELECT Entity.id as idx, Entity.geom as geometry, "
             sql_statement += "Q.sum AS damage_probability "
             sql_statement += "FROM "
@@ -324,17 +338,32 @@ class ExposureDatabase(SpatialiteDatabase):
             sql_statement += "WHERE Entity.osm_id IS NULL"
 
         self.connection.execute(sql_statement)
-        logger.debug("View %s created" % view_name.lower())
+        logger.debug("View %s created" % name)
 
         # Insert necessary entry to the `view_geometry_columns` table
         sql_statement = "INSERT INTO views_geometry_columns "
         sql_statement += "(view_name, view_geometry, view_rowid, "
         sql_statement += "f_table_name, f_geometry_column, read_only) "
-        sql_statement += (
-            "VALUES ('%s', 'geometry', 'idx', 'entity', 'geom', 1)" % view_name.lower()
-        )
+        sql_statement += "VALUES ('%s', 'geometry', 'idx', 'entity', 'geom', 1)" % name
         self.connection.execute(sql_statement)
-        logger.debug("Geometry entry for view %s created" % view_name.lower())
+        logger.debug("Geometry entry for view %s created" % name)
+
+    def view_exists(self, view_name):
+        """
+        Checks if a view with the given name exists in the database.
+
+        Args:
+            view_name (str):
+                Name of the view.
+
+        Returns:
+            True if the view exists, false if not.
+        """
+
+        sql_statement = "SELECT COUNT(name) FROM sqlite_master WHERE type='view' "
+        sql_statement += "AND name='%s'" % view_name.lower()
+        self.cursor.execute(sql_statement)
+        return self.cursor.fetchone()[0] == 1
 
     def delete_view(self, view_name):
         """
@@ -345,12 +374,12 @@ class ExposureDatabase(SpatialiteDatabase):
                 Name of the view to be deleted. The name must be in lower case in the geometry
                 table and will therefore be changed to lower case.
         """
-
-        self.connection.execute("DROP VIEW IF EXISTS %s" % view_name.lower())
+        name = view_name.lower()
+        self.connection.execute("DROP VIEW IF EXISTS %s" % name)
         sql_statement = "DELETE FROM views_geometry_columns "
-        sql_statement += "WHERE view_name = '%s'" % view_name.lower()
+        sql_statement += "WHERE view_name = '%s'" % name
         self.connection.execute(sql_statement)
-        logger.debug("View %s deleted" % view_name.lower())
+        logger.debug("View %s deleted" % name)
 
     def insert_tile_entity(self, quadkey):
         """