does this ST_AsGeoJSON function hardcode itself to look for column names "id"
and "geom" ? it's not going to be any easier to get SQLAlchemy to render "t"
than it is "t.*". it wants to name columns.
On Tue, Apr 14, 2020, at 9:45 AM, Adrien Berchet wrote:
> I just found that in fact it is possible to just pass the table name to
> ST_AsGeoJson, so the following query works:
>> SELECT ST_AsGeoJSON(t)
>> FROM t;
>
> I will try to use this writing in GeoAlchemy2, though I don't know yet how to
> translate it in SQLAlchemy.
>
> Le mar. 14 avr. 2020 à 14:23, Mike Bayer <mike...@zzzcomputing.com> a écrit :
>> __
>> and you can't say "SELECT t.d, t.geom" ? There really should be no
>> difference between "t.*" and "t.id, t.geom".
>>
>>
>>
>> On Tue, Apr 14, 2020, at 5:31 AM, Adrien Berchet wrote:
>>> The "column names" issue is that when we use ROW(), like in the following
>>> query:
>>>> SELECT ROW(t.id, t.geom)
>>>> FROM (SELECT 1 AS id, ST_GeomFromText('POINT( 1 1)') AS geom) AS t;
>>> we obtain the following result:
>>>> row
>>>> ------------------------------------------------
>>>> (1,0101000000000000000000F03F000000000000F03F)
>>> in which the initial column names ('id' and 'geom') are lost. So when we
>>> give this result to the ST_AsGeoJson() function, it can not retrieve these
>>> names for the property names so it just replaces them by 'f1', 'f2', ...
>>>
>>> And I can't find any way to pass the names to the ROW() constructor:
>>> https://www.postgresql.org/docs/current/sql-expressions.html#SQL-SYNTAX-ROW-CONSTRUCTORS
>>>
>>>
>>> Le mardi 14 avril 2020 00:47:28 UTC+2, Mike Bayer a écrit :
>>>>
>>>>
>>>> On Mon, Apr 13, 2020, at 6:25 PM, Adrien Berchet wrote:
>>>>> Hello there
>>>>>
>>>>> I tried to integrate your POC in GeoAlchemy2 in the following PR:
>>>>> https://github.com/geoalchemy/geoalchemy2/pull/258
>>>>>
>>>>> It is almost working but the ST_AsGeoJSON() function needs a record, not
>>>>> a list of columns. So the query should be like:
>>>>>> SELECT ST_AsGeoJSON(t.*)
FROM t;
>>>>> while the example you provided gives:
>>>>>> SELECT ST_AsGeoJSON(t.id, t.geom)
FROM t;
>>>>> which is not accepted by PostGIS (Error: the function
>>>>> st_asgeojson(integer, geometry) does not exist).
>>>>>
>>>>> I was able to make it work in the PR by adding a call to the ROW()
>>>>> function, which leads to the following query:
>>>>>> SELECT ST_AsGeoJSON(ROW(t.id, t.geom))
FROM t;
>>>>> This query is properly executed by PostGIS but the column names are lost.
>>>>> For example I will get the following result:
>>>>>> {"type": "Feature", "geometry": {"type":"Point","coordinates":[1,1]},
>>>>>> "properties": {*"f1"*: 1}} => "f1" property should be name "id"
>>>>> instead of:
>>>>>> {"type": "Feature", "geometry": {"type":"Point","coordinates":[1,1]},
>>>>>> "properties": {*"id"*: 1}}
>>>>>
>>>>> Do you have any idea to overcome this issue? I did not find how to
>>>>> produce a "t.*" with SQLAlchemy...
>>>>
>>>>
>>>> There should definitely be some way for this to work without doing "*".
>>>> what if "t" didn't have the columns in that specific order? the "ROW"
>>>> function seems like what should be used but I don't understand the "column
>>>> names" issue, is this regarding what goes into the JSON structure that the
>>>> PG function returns? there should be a way to affect that at the SQL level.
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>>
>>>>> Thanks :-)
>>>>>
>>>>> ``
>>>>>
>>>>> Le lundi 20 janvier 2020 18:05:31 UTC+1, Mike Bayer a écrit :
>>>>>>
>>>>>>
>>>>>> On Sun, Jan 19, 2020, at 12:23 PM, Stephan Hügel wrote:
>>>>>>>
>>>>>>>
>>>>>>> On Sunday, 19 January 2020 16:13:40 UTC, Mike Bayer wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On Sun, Jan 19, 2020, at 11:10 AM, Mike Bayer wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Sun, Jan 19, 2020, at 10:54 AM, Stephan Hügel wrote:
>>>>>>>>>> I'm trying to define a GenericFunction that calls a PostGIS 3.0
>>>>>>>>>> function (ST_AsGeoJson
>>>>>>>>>> <https://postgis.net/docs/ST_AsGeoJSON.html>). The latest version
>>>>>>>>>> can be called in two different ways:
>>>>>>>>>>
>>>>>>>>>> SELECT ST_AsGeoJSON(t.geom) FROM foo as t WHERE t.id = 1;
>>>>>>>>>> SELECT ST_AsGeoJSON(t.*) FROM foo as t WHERE t.id = 1;
>>>>>>>>>>
>>>>>>>>>> where the first example returns a GeoJSON Geometry, and the second
>>>>>>>>>> returns a GeoJSON Feature. I'm only interested in making use of the
>>>>>>>>>> second type / am happy to define the two variants separately.
>>>>>>>>>>
>>>>>>>>>> I should be able to subclass GenericFunction in order to do this,
>>>>>>>>>> but I'm missing two details:
>>>>>>>>>>
>>>>>>>>>> 1. What should the return type of my subclass be?
>>>>>>>>>> 2. How can I specify that I want to pass the record / row / all
>>>>>>>>>> columns, as opposed to just the geom column to the underlying
>>>>>>>>>> function? Ordinarily, attempting something like
>>>>>>>>>>
>>>>>>>>>> sess.query(func.MyGeojson(Foo)).all()
>>>>>>>>>>
>>>>>>>>>> Will give me an error:
>>>>>>>>>>
>>>>>>>>>> Object <class 'models.Foo'> is not legal as a SQL literal value
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> by "return type" I think you're referring to the "type" attribute, so
>>>>>>>>> in SQL if you were to make a database column that stores the result
>>>>>>>>> of the ST_AsGeoJSON function, a quick google shows it as "text", so
>>>>>>>>> for SQLAlchemy you could make the return type String, VARCHAR, TEXT,
>>>>>>>>> etc.
>>>>>>>>
>>>>>>>> OK well looking at https://postgis.net/docs/ST_AsGeoJSON.html it says
>>>>>>>> "Return the geometry as a GeoJSON "geometry" object, or the row as a
>>>>>>>> GeoJSON "feature" object", even though the signatures say "text". OK
>>>>>>>> so I see you want to change the type based on the arguments. It's safe
>>>>>>>> to do that in your constructor as well; "if
>>>>>>>> this_looks_like_a_row(args): self.type = Feature else:
>>>>>>>> self.type=Geometry".
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>> for the column expansion you override the constructor and inspect the
>>>>>>>>> object(s) given and do what you want with them. SQLAlchemy has some
>>>>>>>>> built-in systems for "how to expand an ORM model or Selectable into
>>>>>>>>> Table columns" but only in 1.4 is there a new system for this that is
>>>>>>>>> organized and predictable, so for the moment you'd want to roll it
>>>>>>>>> yourself:
>>>>>>>>>
>>>>>>>>> from sqlalchemy import inspect
>>>>>>>>>
>>>>>>>>> class MyFunction(GenericFunction):
>>>>>>>>> def __init__(self, *args, **kw):
>>>>>>>>> pass_args = []
>>>>>>>>> for arg in args:
>>>>>>>>> insp = inspect(arg)
>>>>>>>>> if hasattr(insp, "selectable"):
>>>>>>>>> pass_args.extend(selectable.c.)
>>>>>>>>> else:
>>>>>>>>> pass_args.append(arg)
>>>>>>>>> super(MyFunction, self).__init__(*pass_args, **kw)
>>>>>>>>>
>>>>>>>>> also note there's been a lot of call for Geo support lately (not sure
>>>>>>>>> if you were the person that filed an issue re: SQL Server) but we are
>>>>>>>>> really looking for help to get geoalchemy2 up to date and supporting
>>>>>>>>> more backends.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>>> SQLAlchemy -
>>>>>>>>>> The Python SQL Toolkit and Object Relational Mapper
>>>>>>>>>>
>>>>>>>>>> http://www.sqlalchemy.org/
>>>>>>>>>>
>>>>>>>>>> To post example code, please provide an MCVE: Minimal, Complete, and
>>>>>>>>>> Verifiable Example. See http://stackoverflow.com/help/mcve for a
>>>>>>>>>> full description.
>>>>>>>>>> ---
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>>>>>>>>>> To unsubscribe from this group and stop receiving emails from it,
>>>>>>>>>> send an email to sqlal...@googlegroups.com.
>>>>>>>>>> To view this discussion on the web visit
>>>>>>>>>> https://groups.google.com/d/msgid/sqlalchemy/f3718ff7-a252-41a9-8ac4-1ee2ee1e7f9f%40googlegroups.com
>>>>>>>>>>
>>>>>>>>>> <https://groups.google.com/d/msgid/sqlalchemy/f3718ff7-a252-41a9-8ac4-1ee2ee1e7f9f%40googlegroups.com?utm_medium=email&utm_source=footer>.
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>> Thanks for the quick response Mike!
>>>>>>>
>>>>>>> OK so far I've got:
>>>>>>> https://gist.github.com/urschrei/782989d0b3bee8e4208eb2bea945b65b.
>>>>>>> Requires PostGIS 3.0.x as an extension, and requires GeoAlchemy2.
>>>>>>>
>>>>>>> On line 15, I fixed what I assume was a typo for selectable in your
>>>>>>> original suggestion. I still get the expected
>>>>>>>
>>>>>>> Object <class '__main__.Hardinfra'> is not legal as a SQL literal value
>>>>>>>
>>>>>>> error though. I don't follow your suggestion about
>>>>>>>
>>>>>>> "if this_looks_like_a_row(args): self.type = Feature else:
>>>>>>> self.type=Geometry"
>>>>>>
>>>>>> that was pseudocode. If the incoming argument is a "selectable", that
>>>>>> is, has a .c attribute, it's a set of columns, therefore, it's a row.
>>>>>> otherwise, it's not.
>>>>>>
>>>>>> Here's complete POC
>>>>>>
>>>>>> from sqlalchemy import Column
>>>>>> from sqlalchemy import func
>>>>>> from sqlalchemy import inspect
>>>>>> from sqlalchemy import Integer
>>>>>> from sqlalchemy import String
>>>>>> from sqlalchemy.ext.declarative import declarative_base
>>>>>> from sqlalchemy.sql.functions import GenericFunction
>>>>>> from sqlalchemy.types import UserDefinedType
>>>>>>
>>>>>>
>>>>>> class Feature(UserDefinedType):
>>>>>> pass
>>>>>>
>>>>>>
>>>>>> class Geometry(UserDefinedType):
>>>>>> pass
>>>>>>
>>>>>>
>>>>>> class MyGj(GenericFunction):
>>>>>> def __init__(self, *args, **kw):
>>>>>> pass_args = []
>>>>>> for arg in args:
>>>>>> insp = inspect(arg)
>>>>>> if hasattr(insp, "selectable"):
>>>>>> pass_args.extend(insp.selectable.c)
>>>>>> self.type = Feature
>>>>>> else:
>>>>>> self.type = Geometry
>>>>>> pass_args.append(arg)
>>>>>> super(MyGj, self).__init__(*pass_args, **kw)
>>>>>>
>>>>>> name = "ST_AsGeoJson"
>>>>>>
>>>>>>
>>>>>> Base = declarative_base()
>>>>>>
>>>>>>
>>>>>> class A(Base):
>>>>>> __tablename__ = "a"
>>>>>>
>>>>>> id = Column(Integer, primary_key=True)
>>>>>> data = Column(String)
>>>>>>
>>>>>>
>>>>>> function = func.ST_AsGeoJson(A)
>>>>>>
>>>>>> assert isinstance(function.type, Feature)
>>>>>>
>>>>>>
>>>>>> print(function)
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> possibly because I'm not well-versed in SQLA's internals – is there an
>>>>>>> easy way to distinguish between a row and a column? That still leaves
>>>>>>> the issue of the "Geometry" vs "Feature" distinction in self.types:
>>>>>>> Geoalchemy2 defines a "Geometry" type, but not a "Feature" type,
>>>>>>> because "Feature" is only a part of the GeoJSON spec, but I doubt that
>>>>>>> either of these things are causing the problem. I've also tried
>>>>>>> executing the SQL query on my db to make sure it's working and both
>>>>>>>
>>>>>>> SELECT ST_AsGeoJSON(t.*) FROM hardinfra as t WHERE t.id = 1;
>>>>>>> SELECT ST_AsGeoJSON(t.geom) FROM hardinfra as t WHERE t.id = 1;
>>>>>>>
>>>>>>> work, returning a GeoJSON Feature and Geometry respectively.
>>>>>>>
>>>>>>> I didn't open the issue about SQL Server, but I use GeoAlchemy
>>>>>>> regularly, so if there are intro issues available I'm happy to help out
>>>>>>> when I can.
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> SQLAlchemy -
>>>>>>> The Python SQL Toolkit and Object Relational Mapper
>>>>>>>
>>>>>>> http://www.sqlalchemy.org/
>>>>>>>
>>>>>>> To post example code, please provide an MCVE: Minimal, Complete, and
>>>>>>> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
>>>>>>> description.
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>>>>>>>
>>>>>>> <https://groups.google.com/d/msgid/sqlalchemy/795a8d14-17da-4c47-a917-78f355e88951%40googlegroups.com?utm_medium=email&utm_source=footer>.
>>>>>>
>>>>>
>>>>> --
>>>>> SQLAlchemy -
>>>>> The Python SQL Toolkit and Object Relational Mapper
>>>>>
>>>>> http://www.sqlalchemy.org/
>>>>>
>>>>> To post example code, please provide an MCVE: Minimal, Complete, and
>>>>> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
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>>>>>
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>>>>
>>>
>>> --
>>> SQLAlchemy -
>>> The Python SQL Toolkit and Object Relational Mapper
>>>
>>> http://www.sqlalchemy.org/
>>>
>>> To post example code, please provide an MCVE: Minimal, Complete, and
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>>
>>
>> --
>> SQLAlchemy -
>> The Python SQL Toolkit and Object Relational Mapper
>>
>> http://www.sqlalchemy.org/
>>
>> To post example code, please provide an MCVE: Minimal, Complete, and
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>
> --
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>
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