[sqlalchemy] Automap errors: one or more mappers failed to initialize, property of that name exists on mapper

[Liu Shengpeng]

Base = automap_base()
engine = create_engine("sqlite:///xx.sqlite")

Base.prepare(engine, reflect=True)
session = Session(engine)

Item = Base.classes["items"]

for item in session.query(Item).limit(10):
print(item)


error occurs:

InvalidRequestError: One or more mappers failed to initialize - can't proceed with initialization of other mappers. Triggering mapper: 'Mapper|items|items'. Original exception was: Error creating backref 'items_collection' on relationship 'items.items_collection': property of that name exists on mapper 'Mapper|items|items'
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http://www.sqlalchemy.org/

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[mike bayer]

Hello -

For future issues of this nature, please take care to include the table
definition that is being reflected, so that others can help to answer
this question. I had to deduce backwards what the problem would be
here, it is a table of this form:

engine.execute("""
create table item (
id integer,
primary key (id)
)
""")
engine.execute("""
create table item_to_item (
item_a_id integer,
item_b_id integer,
primary key (item_a_id, item_b_id),
foreign key (item_a_id) references item(id),
foreign key (item_b_id) references item(id)
)
""")


You need to use a naming convention to break the name overlap (e.g.
http://docs.sqlalchemy.org/en/latest/orm/extensions/automap.html#overriding-naming-schemes):

def make_collection_name(base, local_cls, referred_cls, constraint):
if local_cls is referred_cls:
return constraint.columns.keys()[0] + "_collection"


this would produce collections of the name "item_a_id_collection" and
"item_b_id_collection". You might want to hardcode a lookup table with
more convenient names.

Post by Liu Shengpeng
Base = automap_base()
engine = create_engine("sqlite:///xx.sqlite")
Base.prepare(engine, reflect=True)
session = Session(engine)
Item = Base.classes["items"]
print(item)
InvalidRequestError: One or more mappers failed to initialize - can't
'Mapper|items|items'. Original exception was: Error creating backref
'items_collection' on relationship 'items.items_collection': property of
that name exists on mapper 'Mapper|items|items'
--
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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http://www.sqlalchemy.org/

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