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
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> .
>
>
>
>
> 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
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> .
>
>
>
> --
> SQLAlchemy -
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>
> 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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>
>
> --
> 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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