add example for delete callback

Author: lonvia

flex-config/track-changes.lua

@@ -0,0 +1,80 @@
+-- This config example file is released into the Public Domain.
+
+-- This config shows how to track in a table which OSM object have been
+-- added, changed and deleted.
+
+-- The main table logging the changes.
+local change_table = osm2pgsql.define_table{
+    name = 'change_log',
+    -- Disable automatic ID tracking by osm2pgsql. No rows should ever
+    -- be deleted. osm2pgsql will issue a warning about this. It can
+    -- be safely ignored.
+    ids = nil,
+    columns = {
+        { column = 'osm_type', type = 'text' },
+        { column = 'osm_id', type = 'bigint' },
+        { column = 'version', type = 'int' },
+        -- This column describes the kind of change:
+        -- 'A' for added/newly created,
+        -- 'M' for modified,
+        -- 'D' for deleted
+        { column = 'action', type = 'text' },
+        { column = 'date', sql_type = 'timestamp' }
+    },
+    indexes = {
+        { column = { 'osm_type', 'osm_id' }, method = 'btree' }
+    }
+}
+
+-- We only want to catch changes coming from the OSM file input.
+-- This flag marks when file reading is done and dependent objects are
+-- being processed.
+local file_reading_in_progress = true
+
+local function format_date(ts)
+    return os.date('!%Y-%m-%dT%H:%M:%SZ', ts)
+end
+
+local function add_object_change(object)
+    -- In this example only changes while updating the database are recorded.
+    -- This happens in 'append' mode.
+    if osm2pgsql.mode == 'append' and file_reading_in_progress then
+        change_table:insert{
+            osm_type = object.type,
+            osm_id = object.id,
+            version = object.version,
+            action = (object.version == 1) and 'A' or 'M',
+            date = format_date(object.timestamp)
+        }
+    end
+end
+
+osm2pgsql.process_node = add_object_change
+osm2pgsql.process_way = add_object_change
+osm2pgsql.process_relation = add_object_change
+
+osm2pgsql.process_untagged_node = add_object_change
+osm2pgsql.process_untagged_way = add_object_change
+osm2pgsql.process_untagged_relation = add_object_change
+
+
+local function add_deleted_object(object)
+    change_table:insert{
+        osm_type = object.type,
+        osm_id = object.id,
+        version = object.version,
+        action = 'D',
+        date = format_date(object.timestamp)
+    }
+end
+
+osm2pgsql.process_deleted_node = add_deleted_object
+osm2pgsql.process_deleted_way = add_deleted_object
+osm2pgsql.process_deleted_relation = add_deleted_object
+
+function osm2pgsql.after_relations()
+  -- This callback is called after the last relation has been read from
+  -- the input file. As objects are guaranteed to come in order
+  -- node/way/relation, file reading is done at that point.
+  file_reading_in_progress = false
+end