Error: Spatial queries sent to the OEP API using oedialect and a payload containing crs as a string (“4326”) fail.

[jh-RLI]

Users reported to me that they run into a strange error when they run dingo and want to get the data from the OEP. There the error log is:

ERROR 09/Sep/2025 19:10:11,597 log Internal Server Error: /api/v0/advanced/search
....
psycopg2.errors.InternalError_: could not parse proj string '4326'
CONTEXT:  SQL function "st_transform" statement 1

Here sqlachemy + oedialect are involved. I knew that there are issues with the oedialect so it took me some time to figure out what the issue is. As the error states there is some place in your code where the CRS is expected as int value but is availabe as string.

TO verify that i tried to run a request against the OEP using a similar query. Using the code below ... which worked perfectly:

Note the 4326 which is given as int value. If you change that to string the same error is raised.

import requests




PRODCTION_OEP_URL = "https://openenergyplatform.org"


PRODCTION_HEADER = {"Authorization": "Token *********"}

REST_API = "/api/v0"
ADVANCED_API = "/api/v0/advanced/search"
ADVANCED_API_COlUMNS = "/api/v0/advanced/get_columns"


if USE_LOCAL:
    pass

if not USE_LOCAL:
    query = {
        "fields": [
            {
                "type": "function",
                "function": "ST_AsGeoJSON",
                "operands": [
                    {
                        "type": "function",
                        "function": "ST_Transform",
                        "operands": [{"type": "column", "column": "geom"}, 4326],
                    }
                ],
            }
        ],
        "from": {"type": "table", "table": "ego_grid_ding0_mv_grid", "schema": "grid"},
    }

    response = requests.post(
        url=f"{PRODCTION_OEP_URL}{ADVANCED_API}",
        # headers=PRODCTION_HEADER,
        json={"query": query},
    )


print(response.json())
# print(response.json()["data"])
print(response.reason)

Then i set up ding0 locally using python 3.8 to debug this further. When i print out the data ding0 attempts to send to in the request to the oep i see that CRS is given as string ("4326") value. I stopped here, maybe this is a good hint for you @nesnoj where this happens?:

Internal Server Error advanced/search {
    "query": {
        "type": "select",
        "distinct": true,
        "fields": [
            {
                "type": "column",
                "column": "subst_id",
                "is_literal": false,
                "table": "ego_dp_mv_griddistrict",
                "schema": "grid"
            },
            {
                "type": "label",
                "element": {
                    "type": "function",
                    "function": "ST_AsText",
                    "operands": {
                        "type": "grouping",
                        "grouping": [
                            {
                                "type": "function",
                                "function": "ST_Transform",
                                "operands": {
                                    "type": "grouping",
                                    "grouping": [
                                        {
                                            "type": "column",
                                            "column": "geom",
                                            "is_literal": false,
                                            "table": "ego_dp_mv_griddistrict",
                                            "schema": "grid"
                                        },
                                        "4326"
                                    ]
                                }
                            }
                        ]
                    }
                },
                "label": "poly_geom"
            },
            {
                "type": "label",
                "element": {
                    "type": "function",
                    "function": "ST_AsText",
                    "operands": {
                        "type": "grouping",
                        "grouping": [
                            {
                                "type": "function",
                                "function": "ST_Transform",
                                "operands": {
                                    "type": "grouping",
                                    "grouping": [
                                        {
                                            "type": "column",
                                            "column": "point",
                                            "is_literal": false,
                                            "table": "ego_dp_hvmv_substation",
                                            "schema": "grid"
                                        },
                                        "4326"
                                    ]
                                }
                            }
                        ]
                    }
                },
                "label": "subs_geom"
            }
        ],
        "from": [
            {
                "type": "join",
                "join_type": "JOIN ",
                "left": {
                    "type": "table",
                    "schema": "grid",
                    "table": "ego_dp_mv_griddistrict"
                },
                "right": {
                    "type": "table",
                    "schema": "grid",
                    "table": "ego_dp_hvmv_substation"
                },
                "on": {
                    "type": "operator",
                    "operands": [
                        {
                            "type": "column",
                            "column": "subst_id",
                            "is_literal": false,
                            "table": "ego_dp_mv_griddistrict",
                            "schema": "grid"
                        },
                        {
                            "type": "column",
                            "column": "subst_id",
                            "is_literal": false,
                            "table": "ego_dp_hvmv_substation",
                            "schema": "grid"
                        }
                    ],
                    "operator": " = "
                }
            }
        ],
        "where": {
            "type": "operator",
            "operator": " AND ",
            "operands": [
                {
                    "type": "operator",
                    "operator": " AND ",
                    "operands": [
                        {
                            "type": "operator",
                            "operands": [
                                {
                                    "type": "column",
                                    "column": "subst_id",
                                    "is_literal": false,
                                    "table": "ego_dp_mv_griddistrict",
                                    "schema": "grid"
                                },
                                {
                                    "type": "grouping",
                                    "grouping": [
                                        460
                                    ]
                                }
                            ],
                            "operator": " IN "
                        },
                        {
                            "type": "operator",
                            "operands": [
                                {
                                    "type": "column",
                                    "column": "version",
                                    "is_literal": false,
                                    "table": "ego_dp_mv_griddistrict",
                                    "schema": "grid"
                                },
                                "v0.4.5"
                            ],
                            "operator": " = "
                        }
                    ]
                },
                {
                    "type": "operator",
                    "operands": [
                        {
                            "type": "column",
                            "column": "version",
                            "is_literal": false,
                            "table": "ego_dp_hvmv_substation",
                            "schema": "grid"
                        },
                        "v0.4.5"
                    ],
                    "operator": " = "
                }
            ]
        },
        "connection_id": 7574262158457431796,
        "cursor_id": 1067332787219545109
    },
    "connection_id": 7574262158457431796,
    "cursor_id": 1067332787219545109
}

[jh-RLI]

While investigating another issue in the OEP API came across this error again. Here is more more explaination why this happens:

The diagnosis is confirmed, and it is on the ding0 side — but the OEP was
hiding the evidence, which is why this was hard to act on.
ST_Transform has four overloads. With the target reference system as an
integer postgres resolves (geometry, integer) and reprojects. With it as
a string it resolves (geometry, to_proj text)instead, and PROJ then
tries to read 4326 as a projection definition — hence could not parse proj string '4326'. Verified against PostGIS 3.4:

second argument	resolved overload	outcome
4326	geometry, integer	reprojects
'4326'	geometry, to_proj text	could not parse proj string '4326'

So the fix here is to send the SRID as a JSON number rather than a string.
On our side: the API was answering Invalid request and throwing PostGIS'
message away, so nothing in the response pointed at the SRID argument. That is
fixed — the projection error now reaches the client, and the same request will
tell you what is wrong. (The 500> in your original traceback is also gone; it
had already become a 400 in the meantime, just an unhelpful one.)
We are not going to coerce numeric strings to integers on the platform side.
The Advanced Query API deliberately forwards function calls without knowing
their signatures, and a coercion rule that guessed would change the meaning of
requests that pass numeric strings on purpose.