[sqlalchemy] select distinct on a relation to an entity with composite primary key

[NiL]

hi list,

I have the following (elixir) definitions

class Invoice(Entity):
    user_name = Field(Unicode(255))
    item = ManyToOne(Item)

class Item(Entity):
    item_id = Field(Integer,  primary_key=True)
    service_id = Field(Unicode(255),  primary_key=True)
    item_class = Field(Unicode(255),  primary_key=True)

I wish to select invoices that have distinct items

(Pdb) Session.query(Invoice.item.distinct())
*** RuntimeError: maximum recursion depth exceeded while calling a
Python object

this works
(Pdb) Session.query(Invoice.item_item_id.distinct())
<sqlalchemy.orm.query.Query object at 0x988e7ec>
but doesn't lead to the expected result

here is the invoice's table description

CREATE TABLE invoice (
        id INTEGER NOT NULL,
        user_name VARCHAR(255),
        item_item_id INTEGER,
        item_service_id VARCHAR(255),
        item_item_class VARCHAR(255),
        PRIMARY KEY (id),
        CONSTRAINT invoice_item_item_id_item_service_id_item_item_class_fk
FOREIGN KEY(item_item_id, item_service_id, item_item_class) REFERENCES
item (item_id, service_id, item_class)
)


How can I achieve my query ?

regards
NIL

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