PostgresDsn multiple hosts without TLD

[levsh]

Initial Checks

• I have searched GitHub for a duplicate issue and I'm sure this is something new
• I have searched Google & StackOverflow for a solution and couldn't find anything
• I have read and followed the docs and still think this is a bug
• I am confident that the issue is with pydantic (not my code, or another library in the ecosystem like FastAPI or mypy)

Description

Hi!
I have two questions:

1. From docs "PostgresDsn: user info required, TLD not required, host required, as of V.10 PostgresDsn supports multiple hosts". User info required but postgresql docs has example "postgresql://host1:123,host2:456/somedb?target_session_attrs=any&application_name=myapp"
2. It seems PostgresDsn doesn't work properly with multiple hosts without TLD

Thank you

Example Code

In [1]: import pydantic
   ...: from pydantic import BaseModel, PostgresDsn
   ...: 
   ...: class M(BaseModel):
   ...:     url: PostgresDsn
   ...: 

# Not ok
In [2]: M(url="postgresql://host1:123,host2:456/somedb?target_session_attrs=any&application_name=myapp")
---------------------------------------------------------------------------
ValidationError                           Traceback (most recent call last)
Cell In [2], line 1
----> 1 M(url="postgresql://host1:123,host2:456/somedb?target_session_attrs=any&application_name=myapp")

File ~/.local/share/virtualenvs/.../lib/python3.8/site-packages/pydantic/main.py:342, in pydantic.main.BaseModel.__init__()

ValidationError: 1 validation error for M
url
  userinfo required in URL but missing (type=value_error.url.userinfo)

# Not ok
In [3]: M(url="postgresql://u:p@host1:123,host2:456/somedb?target_session_attrs=any&application_name=myapp")
---------------------------------------------------------------------------
ValidationError                           Traceback (most recent call last)
Cell In [3], line 1
----> 1 M(url="postgresql://u:p@host1:123,host2:456/somedb?target_session_attrs=any&application_name=myapp")

File ~/.local/share/virtualenvs/.../lib/python3.8/site-packages/pydantic/main.py:342, in pydantic.main.BaseModel.__init__()

ValidationError: 1 validation error for M
url
  build() needs keyword-only argument host (type=type_error)

# Add .com
# Ok
In [4]: M(url="postgresql://u:p@host1.com:123,host2.com:456/somedb?target_session_attrs=any&application_name=myapp")
Out[4]: M(url=PostgresDsn('postgresql://u:p@host1.com:123,host2.com:456/somedb?target_session_attrs=any&application_name=myapp', ))

Python, Pydantic & OS Version

pydantic version: 1.10.2
            pydantic compiled: True
                 install path: /home/vagrant/.local/share/virtualenvs/.../lib/python3.8/site-packages/pydantic
               python version: 3.8.6 (default, Dec 22 2020, 17:04:29)  [GCC 7.5.0]
                     platform: Linux-4.15.0-192-generic-x86_64-with-glibc2.27
     optional deps. installed: ['dotenv', 'email-validator', 'typing-extensions']

Affected Components

• Compatibility between releases
• Data validation/parsing
• Data serialization - .dict() and .json()
• JSON Schema
• Dataclasses
• Model Config
• Field Types - adding or changing a particular data type
• Function validation decorator
• Generic Models
• Other Model behaviour - construct(), pickling, private attributes, ORM mode
• Plugins and integration with other tools - mypy, FastAPI, python-devtools, Hypothesis, VS Code, PyCharm, etc.

[samuelcolvin]

There are a couple of problems here.

1. PostgresDsn(...) has some slightly weird behaviour and isn't expected to work like this. I agree that this is very confusing, it should either work properly, or fail completely.
2. There are a whole host of problems with URL types see Revert percent encoding in URLs. #4470 for some explanation, basically we run some different logic only if there's a TLD, the problem as per Revert percent encoding in URLs. #4470 is that if we run that logic on all URLs, a whole bunch of tests fail.

The medium term solutions is to move to a dedicated URL validation library in V2, there is'nt really a good short term solution I'm afraid, you might be best to implement your own validation.

[Kludex]

This is already working on V2. 🙏