From 3f7a0ab8df9f1411a9f1ac0e152583bc7bf0c365 Mon Sep 17 00:00:00 2001
From: RamonWill <ramonwilliams@hotmail.co.uk>
Date: Wed, 2 Sep 2020 23:04:06 +0100
Subject: [PATCH] Support for multiple hosts in PostgreSQL connection string

---
 doc/build/changelog/unreleased_13/4392.rst |  7 +++++++
 lib/sqlalchemy/engine/url.py               |  7 +++++++
 test/dialect/postgresql/test_dialect.py    | 19 +++++++++++++++++++
 3 files changed, 33 insertions(+)
 create mode 100644 doc/build/changelog/unreleased_13/4392.rst

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/engine/url.py b/lib/sqlalchemy/engine/url.py
index 6d2f4aa244..763af74fd3 100644
--- a/lib/sqlalchemy/engine/url.py
+++ b/lib/sqlalchemy/engine/url.py
@@ -755,6 +755,13 @@ def _parse_rfc1738_args(name):
             query = None
         components["query"] = query
 
+        if components["query"]:
+            if "host" in components["query"]:
+                if not isinstance(components["query"]["host"], str):
+                    components["query"]["host"] = ",".join(
+                        components["query"]["host"]
+                    )
+
         if components["username"] is not None:
             components["username"] = _rfc_1738_unquote(components["username"])
 
diff --git a/test/dialect/postgresql/test_dialect.py b/test/dialect/postgresql/test_dialect.py
index 6eaa3295b9..140e19b17a 100644
--- a/test/dialect/postgresql/test_dialect.py
+++ b/test/dialect/postgresql/test_dialect.py
@@ -158,6 +158,25 @@ 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"
-- 
2.47.3