Full text support in peewee

Adds support for full text search in peewee with the creation of two new field types: `FullIndexedCharField` and `FullIndexedTextField`.

Note that this change depends upon https://github.com/zzzeek/sqlalchemy/pull/339

[Delivers #137453279]
[Delivers #137453317]

data/text.py

@@ -0,0 +1,38 @@
+from peewee import Clause, SQL, fn, TextField, Field
+
+def _escape_wildcard(search_query):
+  """ Escapes the wildcards found in the given search query so that they are treated as *characters*
+      rather than wildcards when passed to a LIKE or ILIKE clause with an ESCAPE '!'.
+  """
+  search_query = (search_query
+                  .replace('!', '!!')
+                  .replace('%', '!%')
+                  .replace('_', '!_')
+                  .replace('[', '!['))
+  return search_query
+
+
+def prefix_search(field, prefix_query):
+  """ Returns the wildcard match for searching for the given prefix query. """
+  # Escape the known wildcard characters.
+  prefix_query = _escape_wildcard(prefix_query)
+  return Field.__pow__(field, Clause(prefix_query + '%', SQL("ESCAPE '!'")))
+
+
+def match_mysql(field, search_query):
+  """ Generates a full-text match query using a Match operation, which is needed for MySQL.
+  """
+  if field.name.find('`') >= 0: # Just to be safe.
+    raise Exception("How did field name '%s' end up containing a backtick?" % field.name)
+
+  return Clause(fn.MATCH(SQL("`%s`" % field.name)), fn.AGAINST(SQL('%s', search_query)),
+                parens=True)
+
+
+def match_like(field, search_query):
+  """ Generates a full-text match query using an ILIKE operation, which is needed for SQLite and
+      Postgres.
+  """
+  escaped_query = _escape_wildcard(search_query)
+  clause = Clause('%' + escaped_query + '%', SQL("ESCAPE '!'"))
+  return Field.__pow__(field, clause)