trigger dao added

app/app/dao/trigger/trigger.py

+from app.helpers.misc import with_psql
+import ast
+
+# expr has a form of list [variable, operand, value]
+@with_psql
+def create(cur, appkey, devid, nfid, expr):
+    res = create_function(appkey, devid, nfid, expr)
+    
+    if res[0]:
+        query = """
+        CREATE TRIGGER tr_{}_{}_{}
+        AFTER INSERT
+        ON dev_{}_{}
+        FOR EACH ROW
+        EXECUTE PROCEDURE nf_{}_{}_{}()
+        """.format( appkey, devid, nfid,
+                    appkey, devid,
+                    appkey, devid, nfid)
+
+        cur.execute(query)
+       
+        return (True,)
+    return res
+
+@with_psql
+def delete(cur, appkey, devid, nfid):
+    res = delete_function(appkey, devid, nfid)
+    
+    if res[0]:
+        query = """
+        DROP TRIGGER
+            tr_{}_{}_{}
+        """.format(appkey, devid, nfid)
+        
+        cur.execute(query)
+            
+        return (True,)
+    return res
+
+# expr has a form of list [variable, operand, value]
+@with_psql
+def create_function(cur, appkey, devid, nfid, expr):
+    query = """
+    CREATE OR REPLACE FUNCTION
+        nf_{}_{}_{}()
+    RETURNS trigger AS
+    $BODY$
+    BEGIN
+    """.format(appkey, devid, nfid)
+    
+    if expr[1] == 'CHANGES':
+        query += """
+            INSERT INTO 
+                notifications_queue
+            VALUES
+                ({},{},{})
+        """.format(nfid, appkey, devid)
+    else:
+        query += """
+            IF (NEW data->>'{}')::{} {} {} THEN
+                INSERT INTO 
+                    notifications_queue
+                VALUES
+                    ({},{},{});
+            END IF;
+        """.format( expr[0], get_type(expr[2]), expr[1], expr[2]
+                    ndif, appkey, devid)
+    
+    query += """
+        RETURN NEW;
+    END;
+    $BODY$
+
+    LANGUAGE plpgsql VOLATILE
+    COST 100;
+    """
+
+    print(query)
+    cur.execute(query)
+        
+    return (True, )
+
+
+@with_psql
+def delete_function(cur, appkey, devid, nfid):
+    query = """
+    DROP FUNCTION nf_{}_{}_{}()
+    """.format(appkey, devid, nfid)
+
+    cur.execute(query)
+
+    return (True,)
+
+
+# python to postgresql type translation
+#  int   -> int
+#  float -> real
+#  bool  -> bool
+#  str   -> text
+def get_type(tstr):
+    tstr = tstr.strip()
+    try:
+        # int, float, bool
+        t = ast.literal_eval(tstr).__name__
+    except:
+        t = 'text'
+
+    if t == 'float':
+        t = 'real'
+
+    return t