ST_AsBinary is not unique (again)

[nidi]

PostGIS 2 introduced the following behavior again, which has already been resolved in PostGIS 1.5 (see #252):

SELECT ST_AsBinary('POINT(1 2)');

yields

ERROR:  function st_asbinary(unknown) is not unique
LINE 1: SELECT ST_AsBinary('POINT(1 2)');
               ^
HINT:  Could not choose a best candidate function. You might need to add explicit type casts.

Explicit type casts do work:

SELECT ST_AsBinary('POINT(1 2)'::geometry);
                 st_asbinary                  
----------------------------------------------
 \x0101000000000000000000f03f0000000000000040
(1 row)

Is the need of explicitely defining the result intended or a regression? If this behavior is intended, libraries such as geoalchemy would need to change query construction.

[strk]

I think it's intended. Passing an "unknown" to an ST_AsBinary doesn't specify how to interpret the "unknown". Could be a Geography, or a Geometry or a Raster ...

[robe]

I can see this biting a lot of people (heck even our regression tests have issues). I know the solution is for people to fix their apps, but strk -- you think it would be bad if we put in as part of the legacy sql installs

ST_AsBinary(text) , ST_SRID(text) and some of the other common ones. That was the work-around we put in when geography came on the scene. I think we might have taken some of the wrappers out.

At the very least, I guess we should have this in the docs as a breaking change if we don't already.

[erilem]

Here's a query that works with 1.x and does not work with 2.x:

SELECT
  anon.lake_id, ST_AsBinary(anon.lake_geom)
FROM
  (SELECT
     lake.id AS lake_id, ST_AsBinary(lake.geom) AS lake_geom 
   FROM
     lake 
   WHERE
     lake.geom IS NULL
   UNION
   SELECT
     lake.id AS lake_id, ST_AsBinary(lake.geom) AS lake_geom 
   FROM
     lake 
   WHERE
     lake.geom IS NOT NULL
  ) AS anon;

The error:

function st_asbinary(bytea) is not unique
LINE1: SELECT anon.lake_id, ST_AsBinary(anon...
HINT:  Could not choose a best candidate function. You might need to add explicit type casts.

[robe]

Did you install the legacy.sql script? I suspect I may not have added them to legacy since we never came to a consensus what to do.

We decided to take out the overload function and just consider it a legacy issue. It's bad practice to rely on it since raster, geography, and geometry all have ST_AsBinary functions in 2+. I'm willing ot add it to the legacy script though since I think it could bite a lot of people.

[erilem]

I did not install legacy.sql. But I get the same error with legacy.sql installed in my db.

[erilem]

So this ticket's description reports about

SELECT ST_AsBinary('POINT(1 2)');

failing with this error:

ERROR:  function ST_AsBinary(unknown) is not unique

I've myself reported on a UNION-based query that also fails with a similar, though different error:

ERROR:  function ST_AsBinary(bytea) is not unique

Here's a simpler query that triggers the same error:

SELECT As_AsBinary(ST_AsBinary(ST_GeomFromText('POINT(1 2)')));

ST_AsBinary returns a bytea, which is a type that ST_AsBinary does no longer accept as its input argument.

[erilem]

ST_AsText behaves differently, as it does accept text as input:

SELECT ST_AsText('POINT(1 2)');
 st_astext  
------------
 POINT(1 2)
(1 row)

But this is not documented in ​http://postgis.refractions.net/documentation/manual-2.0/ST_AsText.html.

[robe]

Do we want to add this to legacy or just consider it a documentation bug?

[robe]

Since no one has an opinion I went ahead and added to legacy_minimal. 2.0 at r10736

2.1 at r10737