I Have a project built in django and it uses a postgres database.
This database was populated by CSVs files. So when I want to insert a new object I got the error "duplicated key" because the object with id = 1 already exists.
The code :
user = User(name= "Foo")
user.save()
The table users has the PK on the id.
Indexes:
"users_pkey" PRIMARY KEY, btree (id)
If I get the table's details in psql I got:
Column| Type | Modifiers
------+-------- +--------------------------------------
id | integer | not null default nextval('users_id_seq'::regclass)
Additionally, if I do user.dict after create the variable user and before saving it, I get 'id': None
How can I save the user with an id that is not being used?
You most likely inserted your Users from the CSV setting the id value explicitly, when this happens the postgres sequence is not updated and as a result of that when you try to add a new user the sequence generates an already used value
Check this other question for reference postgres autoincrement not updated on explicit id inserts
The solution is what the answer for that question says, update your sequence manually
You can fix it by setting users_id_seq manually.
SELECT setval('users_id_seq', (SELECT MAX(id) from "users"));
Unless you have name as a primary key for the table the above insert should work. If you have name as primary key remove it and try it.
In Postgres SQL you can specify id as serial and you can mark it as Primary Key.Then whenever you will insert record , it will be in a sequence.
i.e id serial NOT NULL and
CONSTRAINT primkey PRIMARY KEY (id).
As you said its a pre populated by CSV , so when you insert it from python code it will automatically go the end of the table and there will be no duplicate values.
Related
I am trying to write some data to a table in a database which I am creating.
However, I am facing with an integrity error like:
sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) PRIMARY KEY must be unique
My question is how to avoid these errors as I will run a couple of times the script
Basically you are creating an object with an already existing primary key, and it's not accepted by SQLite. Verify it by querying the db with something like
select * from airport where id = 6256
If the query returns a result, you need to change the id of the airport you are saving. Since you use the autoincrement, you don't need to specify an id and the DBMS will assign the next free id in that table.
I am doing an INSERT into a postgres DB, which has an auto increment field called id.
How do I get the value of id after doing the insert in Python? There are good references on this site to this for MySQL databases (i.e. using cursor.lastrowid, or connection.insert_id()) but these don't seem to work with my postgres DB.
The id field is using a sequence to auto increment. So the id field is not null, default, nextval('table_id_seq')
Thanks
Pls try that:
cursor.execute("INSERT INTO .... RETURNING
id_of_new_row = cursor.fetchone()[0]
I'm working with sqlite3 on python 2.7 and I am facing a problem with a many-to-many relationship. I have a table from which I am fetching its primary key like this
current.execute("SELECT ExtensionID FROM tblExtensionLookup where ExtensionName = ?",[ext])
and then i am fetching another primary key from another table
current.execute("SELECT HostID FROM tblHostLookup where HostName = ?",[host])
now what i am doing is i have a third table with these two keys as foreign keys and i inserted them like this
current.execute("INSERT INTO tblExtensionHistory VALUES(?,?)",[Hid,Eid])
The problem is i don't know why but the last insertion is not working it keeps giving errors. Now what i have tried is:
First I thought it was because I have an autoincrement primary id for the last mapping table which I didn't provide, but isn't it supposed to consider itself as it's auto incremented? However I went ahead and tried adding Null,None,0 but nothing works.
Secondly I thought maybe because i'm not getting the values from tables above so I tried printing it out and it shows so it works.
Any suggestions what I am doing wrong here?
EDIT :
When i don't provide primary key i get error as
The table has three columns but you provided only two values
and when i do provide them as None,Null or 0 it says
Parameter 0 is not supported probably because of unsupported type
I tried implementing the #abarnet way but still keeps saying parameter 0 not supported
connection = sqlite3.connect('WebInfrastructureScan.db')
with connection:
current = connection.cursor()
current.execute("SELECT ExtensionID FROM tblExtensionLookup where ExtensionName = ?",[ext])
Eid = current.fetchone()
print Eid
current.execute("SELECT HostID FROM tblHostLookup where HostName = ?",[host])
Hid = current.fetchone()
print Hid
current.execute("INSERT INTO tblExtensionHistory(HostID,ExtensionID) VALUES(?,?)",[Hid,Eid])
EDIT 2 :
The database schema is :
table 1:
CREATE TABLE tblHostLookup (
HostID INTEGER PRIMARY KEY AUTOINCREMENT,
HostName TEXT);
table2:
CREATE TABLE tblExtensionLookup (
ExtensionID INTEGER PRIMARY KEY AUTOINCREMENT,
ExtensionName TEXT);
table3:
CREATE TABLE tblExtensionHistory (
ExtensionHistoryID INTEGER PRIMARY KEY AUTOINCREMENT,
HostID INTEGER,
FOREIGN KEY(HostID) REFERENCES tblHostLookup(HostID),
ExtensionID INTEGER,
FOREIGN KEY(ExtensionID) REFERENCES tblExtensionLookup(ExtensionID));
It's hard to be sure without full details, but I think I can guess the problem.
If you use the INSERT statement without column names, the values must exactly match the columns as given in the schema. You can't skip over any of them.*
The right way to fix this is to just use the column names in your INSERT statement. Something like:
current.execute("INSERT INTO tblExtensionHistory (HostID, ExtensionID) VALUES (?,?)",
[Hid, Eid])
Now you can skip any columns you want (as long as they're autoincrement, nullable, or otherwise skippable, of course), or provide them in any order you want.
For your second problem, you're trying to pass in rows as if they were single values. You can't do that. From your code:
Eid = current.fetchone()
This will return something like:
[3]
And then you try to bind that to the ExtensionID column, which gives you an error.
In the future, you may want to try to write and debug the SQL statements in the sqlite3 command-line tool and/or your favorite GUI database manager (there's a simple extension that runs in for Firefox if you don't want anything fancy) and get them right, before you try getting the Python right.
* This is not true with all databases. For example, in MSJET/Access, you must skip over autoincrement columns. See the SQLite documentation for how SQLite interprets INSERT with no column names, or similar documentation for other databases.
Background:
The application I am currently developing is in transition from SQLite3 to PostgreSQL. All the data has been successfully migrated, using the .dump from the current database, changing all the tables of the type
CREATE TABLE foo (
id INTEGER NOT NULL,
bar INTEGER,
...
PRIMARY KEY (id),
FOREIGN KEY(bar) REFERENCES foobar (id),
...
);
to
CREATE TABLE foo (
id SERIAL NOT NULL,
bar INTEGER,
...
PRIMARY KEY (id),
FOREIGN KEY(bar) REFERENCES foobar (id) DEFERRABLE,
...
);
and SET CONSTRAINTS ALL DEFERRED;.
Since I am using SQLAlchemy I was expecting things to work smoothly from then on, after of course changing the engine. But the problem seems to be with the autoincrement of the primary key to a unique value on INSERT.
The table, say foo, I am currently having trouble with has 7500+ rows but the sequence foo_id_seq's current value is set on 5(because I have tried the inserts five times now all of which have failed).
Question:
So now my question is that without explicitly supplying the id, in the INSERT statement, how can I make Postgres automatically assign a unique value to the id field if foo? Or more specifically, have the sequence return a unique value for it?
Sugar:
Achieve all that through the SQLAlchemy interface.
Environment details:
Python 2.6
SQLAlchemy 8.2
PostgreSQL 9.2
psycopg2 - 2.5.1 (dt dec pq3 ext)
PS: If anybody finds a more appropriate title for this question please edit it.
Your PRIMARY KEY should be defined to use a SEQUENCE as a DEFAULT, either via the SERIAL convenience pseudo-type:
CREATE TABLE blah (
id serial primary key,
...
);
or an explicit SEQUENCE:
CREATE SEQUENCE blah_id_seq;
CREATE TABLE blah (
id integer primary key default nextval('blah_id_seq'),
...
);
ALTER SEQUENCE blah_id_seq OWNED BY blah.id;
This is discussed in the SQLAlchemy documentation.
You can add this to an existing table:
CREATE SEQUENCE blah_id_seq OWNED BY blah.id;
ALTER TABLE blah ALTER COLUMN id SET DEFAULT nextval('blah_id_seq');
if you prefer to restore a dump then add sequences manually.
If there's existing data you've loaded directly into the tables with COPY or similar, you need to set the sequence starting point:
SELECT setval('blah_id_seq', max(id)+1) FROM blah;
I'd say the issue is likely to be to do with your developing in SQLite, then doing a dump and restoring that dump to PostgreSQL. SQLAlchemy expects to create the schema its self with the appropriate defaults and sequences.
What I recommend you do instead is to get SQLAlchemy to create a new, empty database. Dump the data for each table from the SQLite DB to CSV, then COPY that data into the PostgreSQL tables. Finally, update the sequences with setval so they generate the appropriate values.
One way or the other, you will need to make sure that the appropriate sequences are created. You can do it by SERIAL pseudo-column types, or by manual SEQUENCE creation and DEFAULT setting, but you must do it. Otherwise there's no way to assign a generated ID to the table in an efficient, concurrency-safe way.
Use
alter sequence foo_id_seq restart with 7600
should give you 7601 next time you call the sequence.
http://www.postgresql.org/docs/current/static/sql-altersequence.html
And then subsequent values. Just make sure that you restart it with a value > the last id.
I am trying to add an 'id' primary key column to an already existing MySQL table using alembic. I tried the following...
op.add_column('mytable', sa.Column('id', sa.Integer(), nullable=False))
op.alter_column('mytable', 'id', autoincrement=True, existing_type=sa.Integer(), existing_server_default=False, existing_nullable=False)
but got the following error
sqlalchemy.exc.OperationalError: (OperationalError) (1075, 'Incorrect table definition; there can be only one auto column and it must be defined as a key') 'ALTER TABLE mytable CHANGE id id INTEGER NOT NULL AUTO_INCREMENT' ()
looks like the sql statement generated by alembic did not add PRIMARY KEY at the end of the alter statement. Could I have missed some settings?
Thanks in advance!
I spent some time digging through the alembic source code, and this doesn't seem to be supported. You can specify primary keys when creating a table, but not when adding columns. In fact, it specifically checks and won't let you (link to source):
# from alembic.operations.toimpl.add_column, line 132
for constraint in t.constraints:
if not isinstance(constraint, sa_schema.PrimaryKeyConstraint):
operations.impl.add_constraint(constraint)
I looked around, and adding a primary key to an existing table may result in unspecified behavior - primary keys aren't supposed to be null, so your engine may or may not create primary keys for existing rows. See this SO discussion for more info: Insert auto increment primary key to existing table
I'd just run the alter query directly, and create primary keys if you need to.
op.execute("ALTER TABLE mytable ADD id INT PRIMARY KEY AUTO_INCREMENT;")
If you really need cross-engine compatibility, the big hammer would be to (1) create a new table identical to the old one with a primary key, (2) migrate all your data, (3)delete the old table and (4) rename the new table.
Hope that helps.
You have to remove the primary key that is in the table and then create a new one that includes all columns that you want as the primary key.
eg. In psql use \d <table name> to define the schema, then check the primary key constraint.
Indexes:
"enrollments_pkey" PRIMARY KEY, btree (se_crs_id, se_std_id)
then use this information in alembic
def upgrade():
# ### commands auto generated by Alembic - please adjust! ###
op.add_column('enrollments', sa.Column(
'se_semester', sa.String(length=30), nullable=False))
op.drop_constraint('enrollments_pkey', 'enrollments', type_='primary')
op.create_primary_key('enrollments_pkey', 'enrollments', [
'se_std_id', 'se_crs_id', 'se_semester'])
The results after running \d enrollments should be updated to
Indexes:
"enrollments_pkey" PRIMARY KEY, btree (se_std_id, se_crs_id, se_semester)
This solution worked fine for me.