registries: add support for PostgreSQL-based registry

A filename ending in ".pgsql" indicates the use of PostgreSQL. That file
should be in YAML format and contain entries to specify the use of a pgsql
database.

python/lsst/daf/persistence/registries.py

@@ -41,6 +41,8 @@
 import os
 import astropy.io.fits
 import re
+import yaml
+
 try:
     import sqlite3
     haveSqlite3 = True
@@ -52,6 +54,13 @@
     except ImportError:
         haveSqlite3 = False
 
+# PostgreSQL support
+try:
+    import psycopg2 as pgsql
+    havePgsql = True
+except ImportError:
+    havePgsql = False
+
 
 class Registry(object):
     """The registry base class."""
@@ -73,6 +82,9 @@ def create(location):
         # if re.match(r'.*\.paf', location):
         #     return CalibRegistry(location)
 
+        if location.endswith(".pgsql"):
+            return PgsqlRegistry(location)
+
         # look for an sqlite3 registry
         if re.match(r'.*\.sqlite3', location):
             if not haveSqlite3:
@@ -396,3 +408,78 @@ def __init__(self, location):
         else:
             conn = None
         SqlRegistry.__init__(self, conn)
+
+
+class PgsqlRegistry(SqlRegistry):
+    """A PostgreSQL-based registry"""
+    placeHolder = "%s"
+
+    def __init__(self, location):
+        """Constructor
+
+        Parameters
+        ----------
+        location : `str`
+            Path to PostgreSQL configuration file.
+        """
+        if not havePgsql:
+            raise RuntimeError("Cannot use PgsqlRegistry: could not import psycopg2")
+        config = self.readYaml(location)
+        self._config = config
+        conn = pgsql.connect(host=config["host"], port=config["port"], database=config["database"],
+                             user=config["user"], password=config["password"])
+        SqlRegistry.__init__(self, conn)
+
+    def __del__(self):
+        if self.conn:
+            self.conn.close()
+
+    @staticmethod
+    def readYaml(location):
+        """Read YAML configuration file
+
+        The YAML configuration file should contain:
+        * host : host name for database connection
+        * port : port for database connection
+        * user : user name for database connection
+        * database : database name
+
+        It may also contain:
+        * password : password for database connection
+
+        The optional entries are set to `None` in the output configuration.
+
+        Parameters
+        ----------
+        location : `str`
+            Path to PostgreSQL YAML config file.
+
+        Returns
+        -------
+        config : `dict`
+            Configuration
+        """
+        with open(location) as ff:
+            data = yaml.load(ff)
+        requireKeys = set(["host", "port", "database", "user"])
+        optionalKeys = set(["password"])
+        haveKeys = set(data.keys())
+        if haveKeys - optionalKeys != requireKeys:
+            raise RuntimeError(
+                "PostgreSQL YAML configuration (%s) should contain only %s, and may contain 'password', "
+                "but this contains: %s" %
+                (location, ",".join("'%s'" % key for key in requireKeys),
+                 ",".join("'%s'" % key for key in data.keys()))
+            )
+        for key in optionalKeys:
+            if key not in data:
+                data[key] = None
+
+        return data
+
+    def lookup(self, *args, **kwargs):
+        try:
+            return SqlRegistry.lookup(self, *args, **kwargs)
+        except Exception as exc:
+            self.conn.rollback()
+            raise