short postgres primary keys rails migrations based on https://blog.andyet.com/2016/02/23/generating-shortids-in-postgres/

short-primary-keys.diff

diff --git db/migrate/20170712145519_add_unique_short_id_function.rb db/migrate/20170712145519_add_unique_short_id_function.rb
new file mode 100644
index 0000000..4342d8b
--- /dev/null
+++ db/migrate/20170712145519_add_unique_short_id_function.rb
@@ -0,0 +1,76 @@
+class AddUniqueShortIdFunction < ActiveRecord::Migration[5.1]
+  def up
+    # if needed:
+    # enable_extension 'pgcrypto'
+    #
+    # short id function from:
+    # https://blog.andyet.com/2016/02/23/generating-shortids-in-postgres/
+    unique_short_id_function_sql = <<-EOS
+      -- Create a trigger function that takes no arguments.
+      -- Trigger functions automatically have OLD, NEW records
+      -- and TG_TABLE_NAME as well as others.
+      CREATE OR REPLACE FUNCTION unique_short_id()
+      RETURNS TRIGGER AS $$
+
+       -- Declare the variables we'll be using.
+      DECLARE
+        key TEXT;
+        qry TEXT;
+        found TEXT;
+      BEGIN
+
+        -- generate the first part of a query as a string with safely
+        -- escaped table name, using || to concat the parts
+        qry := 'SELECT id FROM ' || quote_ident(TG_TABLE_NAME) || ' WHERE id=';
+
+        -- This loop will probably only run once per call until we've generated
+        -- millions of ids.
+        LOOP
+
+          -- Generate our string bytes and re-encode as a base64 string.
+          key := encode(gen_random_bytes(6), 'base64');
+
+          -- Base64 encoding contains 2 URL unsafe characters by default.
+          -- The URL-safe version has these replacements.
+          key := replace(key, '/', '_'); -- url safe replacement
+          key := replace(key, '+', '-'); -- url safe replacement
+
+          -- Concat the generated key (safely quoted) with the generated query
+          -- and run it.
+          -- SELECT id FROM "test" WHERE id='blahblah' INTO found
+          -- Now "found" will be the duplicated id or NULL.
+          EXECUTE qry || quote_literal(key) INTO found;
+
+          -- Check to see if found is NULL.
+          -- If we checked to see if found = NULL it would always be FALSE
+          -- because (NULL = NULL) is always FALSE.
+          IF found IS NULL THEN
+
+            -- If we didn't find a collision then leave the LOOP.
+            EXIT;
+          END IF;
+
+          -- We haven't EXITed yet, so return to the top of the LOOP
+          -- and try again.
+        END LOOP;
+
+        -- NEW and OLD are available in TRIGGER PROCEDURES.
+        -- NEW is the mutated row that will actually be INSERTed.
+        -- We're replacing id, regardless of what it was before
+        -- with our key variable.
+        NEW.id = key;
+
+        -- The RECORD returned here is what will actually be INSERTed,
+        -- or what the next trigger will get if there is one.
+        RETURN NEW;
+      END;
+      $$ language 'plpgsql';
+    EOS
+
+    execute(unique_short_id_function_sql)
+  end
+
+  def down
+    execute "DROP FUNCTION unique_short_id();"
+  end
+end
diff --git db/migrate/20170712150121_apply_short_id_function_to_recipes.rb db/migrate/20170712150121_apply_short_id_function_to_recipes.rb
new file mode 100644
index 0000000..c510030
--- /dev/null
+++ db/migrate/20170712150121_apply_short_id_function_to_recipes.rb
@@ -0,0 +1,15 @@
+class ApplyShortIdFunctionToRecipes < ActiveRecord::Migration[5.1]
+  def up
+    execute(%Q{
+      -- We name the trigger "trigger_test_genid" so that we can remove
+      -- or replace it later.
+      -- If an INSERT contains multiple RECORDs, each one will call
+      -- unique_short_id individually.
+      CREATE TRIGGER trigger_recipes_genid BEFORE INSERT ON recipes FOR EACH ROW EXECUTE PROCEDURE unique_short_id();
+    })
+  end
+
+  def down
+    execute("DROP TRIGGER trigger_recipes_genid ON recipes")
+  end
+end