added some hints

CHANGELOG.md

@@ -6,11 +6,12 @@ Version 0.13
 - file_link() now throws an error if path doesn't have a valid volume prefix
 - improved datalinker, also reads volumes from /etc/postgresql-common/pg_datalinker.prefix
 - datalinker prefixes can be managed with `pg_datalinker ( init, list, add, del )` command
-- datalinker can now revert old files from backups
+- datalinker can now revert old files from backups when assigning datalinks with tokens
 - datalinker can now unlink+link in one operation
 - trim trailing / on directory names for FS datalinks for better file name uniqueness
 - dlnewcopy() now stores old token in link
 - dlpreviouscopy() looks for this old token first
+- store curl_head response code in datalink. This helps in finding broken links and such.
 
 Version 0.12
 ------------

datalink.sql

@@ -1106,16 +1106,19 @@ begin
  if not found then
       raise exception 'datalink exception' 
             using errcode = 'HW000',
-	    detail = format('Invalid link control options (%s)',my_lco),
-            hint = 'see table datalink.link_control_options for valid link control options';
+	                detail = format('Invalid link control options (%s)',my_lco),
+                  hint = 'see table datalink.link_control_options for valid link control options';
  end if; 
 
  if my_lco is distinct from co.lco then
    e := format('select count(%I) from %s where %I is not null limit 1',
      my_column_name,cast(my_regclass as text),my_column_name);
    execute e into n;
    if n > 0 then
-     raise exception 'Can''t change link control options; % non-null values present in column "%"',n,my_column_name;
+      raise exception 'datalink exception' 
+            using errcode = 'HW000',
+	                detail = format('Can''t change link control options; %s non-null values present in column "%s"',n,my_column_name),
+                  hint = format('Perhaps you can truncate %s',my_regclass);
    end if;
 
    -- update fdw options with new lco

test/expected/other.out

@@ -53,7 +53,9 @@ NOTICE:  DATALINK DDL:TRIGGER on sample_datalinks3
 update datalink.column_options
    set link_control='FILE', integrity='SELECTIVE'
  where table_name='sample_datalinks3' and column_name='link';
-ERROR:  Can't change link control options; 6 non-null values present in column "link"
+ERROR:  datalink exception
+DETAIL:  Can't change link control options; 6 non-null values present in column "link"
+HINT:  Perhaps you can truncate sample_datalinks3
 CONTEXT:  PL/pgSQL function modlco(regclass,name,dl_lco) line 35 at RAISE
 SQL statement "SELECT datalink.modlco(regclass(old.table_name),old.column_name,my_lco)"
 PL/pgSQL function dl_trigger_options() line 18 at PERFORM