--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/db_schema/audit.sql	Fri Feb 24 14:27:10 2017 +0100
@@ -0,0 +1,221 @@
+-- Based on https://github.com/xdimedrolx/audit-trigger/
+--
+-- which is licensed by "The PostgreSQL License", effectively equivalent to the BSD
+-- license.
+
+SET search_path TO land;
+CREATE TABLE audit_trail(
+      id bigserial primary key,
+      table_name varchar(50) not null,
+      tstamp TIMESTAMP WITHOUT TIME ZONE NOT NULL,
+      action varchar(1) NOT NULL CHECK (action IN ('I','D','U', 'T')),
+      object_id integer not null,
+      row_data JSONB,
+      changed_fields JSONB
+);
+
+CREATE OR REPLACE FUNCTION jsonb_delete_left(a jsonb, b jsonb)
+  RETURNS jsonb AS
+  $BODY$
+       SELECT COALESCE(
+              (
+              SELECT ('{' || string_agg(to_json(key) || ':' || value, ',') || '}')
+              FROM jsonb_each(a)
+              WHERE NOT ('{' || to_json(key) || ':' || value || '}')::jsonb <@ b
+              )
+       , '{}')::jsonb;
+       $BODY$
+LANGUAGE sql IMMUTABLE STRICT;
+COMMENT ON FUNCTION jsonb_delete_left(jsonb, jsonb) IS 'delete matching pairs in second argument from first argument';
+DROP OPERATOR IF EXISTS - (jsonb, jsonb);
+CREATE OPERATOR - ( PROCEDURE = jsonb_delete_left, LEFTARG = jsonb, RIGHTARG = jsonb);
+COMMENT ON OPERATOR - (jsonb, jsonb) IS 'delete matching pairs from left operand';
+
+
+CREATE OR REPLACE FUNCTION jsonb_delete_left(a jsonb, b text[])
+  RETURNS jsonb AS
+  $BODY$
+       SELECT COALESCE(
+              (
+              SELECT ('{' || string_agg(to_json(key) || ':' || value, ',') || '}')
+              FROM jsonb_each(a)
+              WHERE key <> ALL(b)
+              )
+       , '{}')::jsonb;
+       $BODY$
+LANGUAGE sql IMMUTABLE STRICT;
+COMMENT ON FUNCTION jsonb_delete_left(jsonb, text[]) IS 'delete keys in second argument from first argument';
+DROP OPERATOR IF EXISTS - (jsonb, text[]);
+CREATE OPERATOR - ( PROCEDURE = jsonb_delete_left, LEFTARG = jsonb, RIGHTARG = text[]);
+COMMENT ON OPERATOR - (jsonb, text[]) IS 'delete keys from left operand';
+
+
+CREATE OR REPLACE FUNCTION jsonb_delete_left(a jsonb, b text)
+  RETURNS jsonb AS
+  $BODY$
+       SELECT COALESCE(
+              (
+              SELECT ('{' || string_agg(to_json(key) || ':' || value, ',') || '}')
+              FROM jsonb_each(a)
+              WHERE key <> b
+              )
+       , '{}')::jsonb;
+       $BODY$
+LANGUAGE sql IMMUTABLE STRICT;
+COMMENT ON FUNCTION jsonb_delete_left(jsonb, text) IS 'delete key in second argument from first argument';
+DROP OPERATOR IF EXISTS - (jsonb, text);
+CREATE OPERATOR - ( PROCEDURE = jsonb_delete_left, LEFTARG = jsonb, RIGHTARG = text);
+COMMENT ON OPERATOR - (jsonb, text) IS 'delete key from left operand';
+
+
+CREATE OR REPLACE FUNCTION if_modified_func() RETURNS TRIGGER AS $body$
+DECLARE
+    audit_row land.audit_trail;
+    include_values boolean;
+    log_diffs boolean;
+    h_old jsonb;
+    h_new jsonb;
+    excluded_cols text[] = ARRAY[]::text[];
+BEGIN
+    IF TG_WHEN <> 'AFTER' THEN
+        RAISE EXCEPTION 'land.if_modified_func() may only run as an AFTER trigger';
+    END IF;
+
+    -- Do nothing on insert and delete.
+    IF (TG_OP = 'INSERT' OR TG_OP = 'DELETE') THEN
+        RETURN NULL;
+    END IF;
+
+    audit_row = ROW(
+        nextval('land.audit_trail_id_seq'), -- id
+        TG_TABLE_NAME::varchar,             -- table_name
+        current_timestamp,                  -- tstamp
+        substring(TG_OP,1,1),               -- action
+        OLD.id,                             -- object_id
+        NULL, NULL                          -- row_data, changed_fields
+        );
+
+    IF TG_ARGV[1] IS NOT NULL THEN
+        excluded_cols = TG_ARGV[1]::text[];
+    END IF;
+
+    IF (TG_OP = 'UPDATE' AND TG_LEVEL = 'ROW') THEN
+        audit_row.row_data = row_to_json(OLD)::JSONB;
+        audit_row.changed_fields = row_to_json(NEW)::JSONB - audit_row.row_data - excluded_cols;
+        IF audit_row.changed_fields = '{}'::jsonb THEN
+            -- All changed fields are ignored. Skip this update.
+            RETURN NULL;
+        END IF;
+    ELSE
+        RAISE EXCEPTION '[land.if_modified_func] - Trigger func added as trigger for unhandled case: %, %',TG_OP, TG_LEVEL;
+        RETURN NULL;
+    END IF;
+    INSERT INTO land.audit_trail VALUES (audit_row.*);
+    RETURN NULL;
+END;
+$body$
+LANGUAGE plpgsql
+SECURITY DEFINER
+SET search_path = land, public;
+
+CREATE OR REPLACE FUNCTION audit_table(target_table regclass, audit_rows boolean, audit_query_text boolean, ignored_cols text[]) RETURNS void AS $body$
+DECLARE
+  stm_targets text = 'INSERT OR UPDATE OR DELETE OR TRUNCATE';
+  _q_txt text;
+  _ignored_cols_snip text = '';
+BEGIN
+    EXECUTE 'DROP TRIGGER IF EXISTS audit_trigger_row ON ' || quote_ident(target_table::TEXT);
+    EXECUTE 'DROP TRIGGER IF EXISTS audit_trigger_stm ON ' || quote_ident(target_table::TEXT);
+
+    IF audit_rows THEN
+        IF array_length(ignored_cols,1) > 0 THEN
+            _ignored_cols_snip = ', ' || quote_literal(ignored_cols);
+        END IF;
+        _q_txt = 'CREATE TRIGGER audit_trigger_row AFTER INSERT OR UPDATE OR DELETE ON ' ||
+                 quote_ident(target_table::TEXT) ||
+                 ' FOR EACH ROW EXECUTE PROCEDURE land.if_modified_func(' ||
+                 quote_literal(audit_query_text) || _ignored_cols_snip || ');';
+        RAISE NOTICE '%',_q_txt;
+        EXECUTE _q_txt;
+        stm_targets = 'TRUNCATE';
+    ELSE
+    END IF;
+
+    _q_txt = 'CREATE TRIGGER audit_trigger_stm AFTER ' || stm_targets || ' ON ' ||
+             target_table ||
+             ' FOR EACH STATEMENT EXECUTE PROCEDURE land.if_modified_func('||
+             quote_literal(audit_query_text) || ');';
+    RAISE NOTICE '%',_q_txt;
+    EXECUTE _q_txt;
+
+END;
+$body$
+language 'plpgsql';
+
+COMMENT ON FUNCTION audit_table(regclass, boolean, boolean, text[]) IS $body$
+Add auditing support to a table.
+
+Arguments:
+   target_table:     Table name, schema qualified if not on search_path
+   audit_rows:       Record each row change, or only audit at a statement level
+   audit_query_text: Record the text of the client query that triggered the audit event?
+   ignored_cols:     Columns to exclude from update diffs, ignore updates that change only ignored cols.
+$body$;
+
+-- Pg doesn't allow variadic calls with 0 params, so provide a wrapper
+CREATE OR REPLACE FUNCTION audit_table(target_table regclass, audit_rows boolean, audit_query_text boolean) RETURNS void AS $body$
+SELECT audit_table($1, $2, $3, ARRAY[]::text[]);
+$body$ LANGUAGE SQL;
+
+-- And provide a convenience call wrapper for the simplest case
+-- of row-level logging with no excluded cols and query logging enabled.
+--
+CREATE OR REPLACE FUNCTION audit_table(target_table regclass) RETURNS void AS $body$
+SELECT audit_table($1, BOOLEAN 't', BOOLEAN 't');
+$body$ LANGUAGE 'sql';
+
+COMMENT ON FUNCTION audit_table(regclass) IS $body$
+Add auditing support to the given table. Row-level changes will be logged with full client query text. No cols are ignored.
+$body$;
+
+CREATE INDEX probe_id_ndx ON audit_trail(cast("row_data"->>'probe_id' AS int));
+CREATE INDEX messung_id_ndx ON audit_trail(cast("row_data"->>'messung_id' AS int));
+
+-- View for probe audit trail
+CREATE OR REPLACE VIEW audit_trail_probe AS
+SELECT
+    id,
+    table_name,
+    object_id,
+    tstamp,
+    cast(row_data ->> 'messungs_id' AS integer) AS messungs_id,
+    coalesce(cast(row_data ->> 'probe_id' AS integer),
+        (SELECT probe_id FROM messung WHERE id = cast(
+            row_data ->> 'messungs_id' AS integer))) AS probe_id,
+    row_data,
+    changed_fields
+FROM audit_trail;
+
+
+-- View for messung audit trail
+CREATE OR REPLACE VIEW audit_trail_messung AS
+SELECT audit_trail.id,
+    audit_trail.table_name,
+    audit_trail.tstamp,
+    audit_trail.action,
+    audit_trail.object_id,
+    audit_trail.row_data,
+    audit_trail.changed_fields,
+    cast(row_data ->> 'messungs_id' AS int) AS messungs_id
+FROM audit_trail;
+
+
+SELECT audit_table('probe', true, false, '{tree_modified, letzte_aenderung}'::text[]);
+SELECT audit_table('messung', true, false, '{tree_modified, letzte_aenderung, status}'::text[]);
+SELECT audit_table('messwert', true, false, '{tree_modified, letzte_aenderung}'::text[]);
+SELECT audit_table('kommentar_p', true, false, '{tree_modified, letzte_aenderung}'::text[]);
+SELECT audit_table('kommentar_m', true, false, '{tree_modified, letzte_aenderung}'::text[]);
+SELECT audit_table('zusatz_wert', true, false, '{tree_modified, letzte_aenderung}'::text[]);
+SELECT audit_table('ortszuordnung', true, false, '{tree_modified, letzte_aenderung}'::text[]);
+
+SET search_path TO public;