I know my question must be very simple but I couldn’t find any straight answer to it.
I am mapping a table with SQlAlchemy :
from sqlalchemy import Table, Column, Integer, String, MetaData, select
metadata = MetaData()
chicago_schools_manual = Table(
'chicago_schools', metadata,
Column('School ID', Integer, primary_key = True),
Column('Name of School', String))
How to I set up an label for the existing columns above to avoid they current name with spaces?
Bonus question : What is the advantage of mapping as as class instead of mapping as table given that their content/efforts are similar (but a little bigger in class)?
Edit extra doubt:
Can you tell me what is wrong with this statement so I can´t use it for a simple select where?
stmt = select(chicago_schools_manual).where(chicago_schools.columns['Name of School'] == 'Charles').limit(20)
Output exceeds the size limit. Open the full output data in a text editor
---------------------------------------------------------------------------
Exception Traceback (most recent call last)
File c:UsersfabioAppDataLocalProgramsPythonPython310libsite-packagesibm_db_dbi.py:1287, in Cursor._set_cursor_helper(self)
1286 try:
-> 1287 num_columns = ibm_db.num_fields(self.stmt_handler)
1288 except Exception as inst:
Exception: SQLNumResultCols failed: [IBM][CLI Driver][DB2/LINUXX8664] SQL0203N A reference to column "CHICAGO_SCHOOLS.Name of School" is ambiguous. SQLSTATE=42702 SQLCODE=-203
During handling of the above exception, another exception occurred:
ProgrammingError Traceback (most recent call last)
File c:UsersfabioAppDataLocalProgramsPythonPython310libsite-packagessqlalchemyenginebase.py:1819, in Connection._execute_context(self, dialect, constructor, statement, parameters, execution_options, *args, **kw)
1818 if not evt_handled:
-> 1819 self.dialect.do_execute(
[SQL: SELECT chicago_schools."School ID", chicago_schools."Name of School", chicago_schools."Safety Score", chicago_schools."Location"
FROM chicago_schools, chicago_schools
WHERE chicago_schools."Name of School" = ? FETCH FIRST 20 ROWS ONLY]
[parameters: ('Charles',)]
If i use it by the way suggested it works :
stmt = select(chicago_schools_manual.c.Name_of_School).where(chicago_schools_manual.c.Name_of_School == 'Charles').limit(20)
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Answer
You can use key="some_name"
to refer to columns by a name that is different from the actual column name in the table. For example,
from sqlalchemy import create_engine, Table, Column, Integer, String, MetaData, select
engine = create_engine("sqlite://")
metadata = MetaData()
chicago_schools_manual = Table(
"chicago_schools",
metadata,
Column("School ID", Integer, primary_key=True, key="school_id"),
Column("Name of School", String, key="name_of_school"),
)
metadata.create_all(engine)
with engine.begin() as conn:
conn.execute(
chicago_schools_manual.insert(), dict(name_of_school="School #1")
)
"""SQL emitted:
INSERT INTO chicago_schools ("Name of School") VALUES (?)
[generated in 0.00032s] ('School #1',)
"""
with engine.begin() as conn:
results = conn.execute(
select(
chicago_schools_manual.c.school_id,
chicago_schools_manual.c.name_of_school,
)
).all()
print(results) # [(1, 'School #1')]
re: bonus question – See