From 9350627e9c8ce00c7335bfa3b3c377b31322a0be Mon Sep 17 00:00:00 2001
From: Helmut Merz <helmutm@cy55.de>
Date: Wed, 19 Feb 2020 13:20:52 +0100
Subject: [PATCH] control triple creation via an 'instead of insert' trigger on
 vtriples

---
 pgsql/fshow.sql     |  6 ++++++
 pgsql/init.sql      |  3 +++
 pgsql/lbase.sql     | 12 +++++-------
 pgsql/tgtriples.sql | 16 ++++++++++++++++
 pgsql/vtriples.sql  |  9 ++++++---
 5 files changed, 36 insertions(+), 10 deletions(-)
 create mode 100644 pgsql/tgtriples.sql

diff --git a/pgsql/fshow.sql b/pgsql/fshow.sql
index 270a2ce..9ae9c2b 100644
--- a/pgsql/fshow.sql
+++ b/pgsql/fshow.sql
@@ -33,3 +33,9 @@ create or replace function show_text(tid bigint) returns text as $$
   select text from texts
     where texts.id = tid;
 $$ language sql;
+
+
+create or replace function show_type(tid smallint) returns text as $$
+  select dtname from datatypes dt
+    where dt.id = tid;
+$$ language sql stable;
diff --git a/pgsql/init.sql b/pgsql/init.sql
index 5c6b0e7..1dff721 100644
--- a/pgsql/init.sql
+++ b/pgsql/init.sql
@@ -7,5 +7,8 @@
 \i fload.sql
 \i fshow.sql
 
+-- create triggers
+\i tgtriple.sql
+
 -- load data
 \i lbase.sql
diff --git a/pgsql/lbase.sql b/pgsql/lbase.sql
index 6d7b59a..92db7e7 100644
--- a/pgsql/lbase.sql
+++ b/pgsql/lbase.sql
@@ -21,10 +21,8 @@ select load_datatype('int');
 select load_datatype('decimal');
 select load_datatype('timestamp');
 
--- basic triples: type assignments for 
--- type -> Property; Property, Class -> Class
-
-select load_triple('node', 'rdf:type', 'rdf:type', 'node', 'rdf:Property', :event);
-select load_triple('node', 'rdf:Property', 'rdf:type', 'node', 'rdfs:Class', :event);
-select load_triple('node', 'rdfs:Class', 'rdf:type', 'node', 'rdfs:Class', :event);
-select load_triple('node', 'rdfs:label', 'rdf:type', 'node', 'rdfs:Property', :event);
+insert into vtriples (stname, stext, ptext, otname, otext, creation) values 
+    ('node', 'rdf:type', 'rdf:type', 'node', 'rdf:Property', :event),
+    ('node', 'rdf:Property', 'rdf:type', 'node', 'rdfs:Class', :event),
+    ('node', 'rdfs:Class', 'rdf:type', 'node', 'rdfs:Class', :event),
+    ('node', 'rdfs:label', 'rdf:type', 'node', 'rdf:Property', :event);
diff --git a/pgsql/tgtriples.sql b/pgsql/tgtriples.sql
new file mode 100644
index 0000000..7571629
--- /dev/null
+++ b/pgsql/tgtriples.sql
@@ -0,0 +1,16 @@
+
+-- create triggers for triples table
+
+create or replace function insert_triple() returns trigger as $$
+  declare
+    trid bigint;
+  begin
+    trid := load_triple(new.stname, new.stext, new.ptext, 
+                        new.otname, new.otext, new.creation);
+    return new;
+  end;
+$$ language plpgsql;
+
+ 
+create trigger insert_triple instead of insert on vtriples
+  for each row execute procedure insert_triple();
diff --git a/pgsql/vtriples.sql b/pgsql/vtriples.sql
index ed42b00..98af7e1 100644
--- a/pgsql/vtriples.sql
+++ b/pgsql/vtriples.sql
@@ -3,9 +3,12 @@
 
 create or replace view vtriples as
 select triples.id,
-       stype, svalue, show_value(stype, svalue) as stext, 
-       predicate, show_value(dt.id, predicate) as ptext, 
-       otype, ovalue, show_value(otype, ovalue) as otext,
+       stype, svalue, predicate, otype, ovalue, creation,
+       show_type(stype) as stname, 
+       show_value(stype, svalue) as stext, 
+       show_value(dt.id, predicate) as ptext, 
+       show_type(otype) as otname,
+       show_value(otype, ovalue) as otext,
        to_char(events.tstamp, 'YYYY-MM-DD HH24:MI:SS') as ts
   from triples, datatypes dt, events
   where dtname = 'node'