From: RamonWill <ramonwilliams@hotmail.co.uk>
Date: Wed, 2 Sep 2020 22:43:53 +0000 (-0400)
Subject: Support for multiple hosts in PostgreSQL connection string
X-Git-Tag: rel_1_4_0b1~64^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f9ef7fd30b3f0613bc9dd912621856b3262d23bc;p=thirdparty%2Fsqlalchemy%2Fsqlalchemy.git

Support for multiple hosts in PostgreSQL connection string

Provide support for multiple hosts in the PostgreSQL connection string.

A user requested for SQLAlchemy to support multiple hosts within a PostgreSQL URL string. The proposed fix allows this. In the event that the url contains multiple hosts the proposed code will convert the query["hosts"] tuple into a single string. This allows the hosts to then get converted into a valid dsn variable in the psycopg2 connect function.

This pull request is:

- [ ] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [X ] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**
Fixes: #4392

Closes: #5554
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/5554
Pull-request-sha: 3f7a0ab8df9f1411a9f1ac0e152583bc7bf0c365

Change-Id: I3f3768d51b8331de786ffdc025b7ecfc662eafe5
---

diff --git a/doc/build/changelog/unreleased_13/4392.rst b/doc/build/changelog/unreleased_13/4392.rst
new file mode 100644
index 0000000000..ecb10ca25d
--- /dev/null
+++ b/doc/build/changelog/unreleased_13/4392.rst
@@ -0,0 +1,7 @@
+.. change::
+    :tags: engine, postgresql, usecase
+    :tickets: 4392
+
+    A :class:`.URL` connection now supports multiple hosts for PostgreSQL. Any
+    query that contains multiple hosts will now group the hosts as a string
+    instead of a tuple of strings. Pull request courtesy Ramon Williams.
diff --git a/lib/sqlalchemy/dialects/postgresql/psycopg2.py b/lib/sqlalchemy/dialects/postgresql/psycopg2.py
index 91576c4d20..3c9ef72c44 100644
--- a/lib/sqlalchemy/dialects/postgresql/psycopg2.py
+++ b/lib/sqlalchemy/dialects/postgresql/psycopg2.py
@@ -71,6 +71,28 @@ using ``host`` as an additional keyword argument::
     `PQconnectdbParams \
     <http://www.postgresql.org/docs/9.1/static/libpq-connect.html#LIBPQ-PQCONNECTDBPARAMS>`_
 
+Multiple Hosts in Connection String
+------------------------
+psycopg2 supports multiple connection points in the connection string.
+When the ``host`` parameter is used multiple times in the query section of
+the URL, SQLAlchemy will create a single string of the host and port
+information provided to make the connections::
+
+    create_engine(
+        "postgresql+psycopg2://user:password@/dbname?host=HostA:port1&host=HostB&host=HostC"
+    )
+
+A connection to each host is then attempted until either a connection is successful
+or all connections are unsuccessful in which case an error is raised.
+
+.. versionadded:: 1.3.20 Support for multiple hosts in PostgreSQL connection
+   string.
+
+.. seealso::
+
+    `PQConnString \
+    <https://www.postgresql.org/docs/10/libpq-connect.html#LIBPQ-CONNSTRING>`_
+
 Empty DSN Connections / Environment Variable Connections
 ---------------------------------------------------------
 
@@ -929,16 +951,25 @@ class PGDialect_psycopg2(PGDialect):
 
     def create_connect_args(self, url):
         opts = url.translate_connect_args(username="user")
+
+        is_multihost = False
+        if "host" in url.query:
+            is_multihost = isinstance(url.query["host"], (list, tuple))
+
         if opts:
             if "port" in opts:
                 opts["port"] = int(opts["port"])
             opts.update(url.query)
+            if is_multihost:
+                opts["host"] = ",".join(url.query["host"])
             # send individual dbname, user, password, host, port
             # parameters to psycopg2.connect()
             return ([], opts)
         elif url.query:
             # any other connection arguments, pass directly
             opts.update(url.query)
+            if is_multihost:
+                opts["host"] = ",".join(url.query["host"])
             return ([], opts)
         else:
             # no connection arguments whatsoever; psycopg2.connect()
diff --git a/test/dialect/postgresql/test_dialect.py b/test/dialect/postgresql/test_dialect.py
index 971d4f12f7..46a01860d5 100644
--- a/test/dialect/postgresql/test_dialect.py
+++ b/test/dialect/postgresql/test_dialect.py
@@ -159,6 +159,25 @@ class DialectTest(fixtures.TestBase):
         eq_(cargs, [])
         eq_(cparams, {"host": "somehost", "any_random_thing": "yes"})
 
+    def test_psycopg2_nonempty_connection_string_w_query_two(self):
+        dialect = psycopg2_dialect.dialect()
+        url_string = "postgresql://USER:PASS@/DB?host=hostA"
+        u = url.make_url(url_string)
+        cargs, cparams = dialect.create_connect_args(u)
+        eq_(cargs, [])
+        eq_(cparams["host"], "hostA")
+
+    def test_psycopg2_nonempty_connection_string_w_query_three(self):
+        dialect = psycopg2_dialect.dialect()
+        url_string = (
+            "postgresql://USER:PASS@/DB"
+            "?host=hostA:portA&host=hostB&host=hostC"
+        )
+        u = url.make_url(url_string)
+        cargs, cparams = dialect.create_connect_args(u)
+        eq_(cargs, [])
+        eq_(cparams["host"], "hostA:portA,hostB,hostC")
+
 
 class ExecuteManyMode(object):
     __only_on__ = "postgresql+psycopg2"