In PostgreSQL, I created a new table and assigned a new sequence to the id column. If I insert a record from the PostgreSQL console it works but when I try to import a record from from Rails, it raises an exception that it is unable to find the associated sequence.
Here is the table:
\d+ user_messages;
Table "public.user_messages"
Column | Type | Modifiers | Storage | Description
-------------+-----------------------------+------------------------------------------------------------+----------+-------------
id | integer | not null default nextval('new_user_messages_id'::regclass) | plain |
But when I try to get the sequence with the SQL query which Rails uses, it returns NULL:
select pg_catalog.pg_get_serial_sequence('user_messages', 'id');
pg_get_serial_sequence
------------------------
(1 row)
The error being raised by Rails is:
UserMessage.import [UserMessage.new]
NoMethodError: undefined method `split' for nil:NilClass
from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:910:in `default_sequence_name'
This problem only occurs when I use the ActiveRecord extension for importing bulk records, single records get saved through ActiveRecord.
How do I fix it?
I think your problem is that you set all this up by hand rather than by using a serial column. When you use a serial column, PostgreSQL will create the sequence, set up the appropriate default value, and ensure that the sequence is owned by the table and column in question. From the fine manual:
pg_get_serial_sequence(table_name, column_name)
get name of the sequence that a serial or bigserial column uses
But you're not using serial or bigserial so pg_get_serial_sequence won't help.
You can remedy this by doing:
alter sequence new_user_messages_id owned by user_messages.id
I'm not sure if this is a complete solution and someone (hi Erwin) will probably fill in the missing bits.
You can save yourself some trouble here by using serial as the data type of your id column. That will create and hook up the sequence for you.
For example:
=> create sequence seq_test_id;
=> create table seq_test (id integer not null default nextval('seq_test_id'::regclass));
=> select pg_catalog.pg_get_serial_sequence('seq_test','id');
pg_get_serial_sequence
------------------------
(1 row)
=> alter sequence seq_test_id owned by seq_test.id;
=> select pg_catalog.pg_get_serial_sequence('seq_test','id');
pg_get_serial_sequence
------------------------
public.seq_test_id
(1 row)
Related
I am using Model.group(:category) in order to get unique records based on category field in Rails 5 application.
Table data:
id catgeory description
1 abc test
2 abc test1
3 abc test2
4 xyz test
5 xyz testabc
I want records (1,4) as a result. Therefore I am using Model.group(:category) which works fine for MYSQL whose sql_mode is " " .
Unforunately its throwing an error "SELECT list is not in GROUP BY clause and contains nonaggregated column which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by" whose sql_mode is "only_full_group_by".
whats the best way to change the query to match the mode?
Perhaps try specifying which id you want? You could use MIN(id), MAX(id) etc.
MySQL supports a non-standard extension to SQL described here. To continue using that behavior, you could change the sql_mode to TRADITIONAL in config/database.yml.
i need your help to finish my delphi homework.
I use ms access database and show all data in 1 dbgrid using sql. I want to show same column but with criteria (50 record per column)
i want select query to produce output like:
No | Name | No | Name |
1 | A | 51 | AA |
2 | B | 52 | BB |
3~50 | | 53~100| |
Is it possible ?
I can foresee issues if you choose to return a dataset with duplicate column names. To fix this, you must change your query to enforce strictly unique column names, using as. For example...
select A.No as No, A.Name as Name, B.No as No2, B.Name as Name2 from TableA A
join TableB B on B.Something = A.Something
Just as a note, if you're using a TDBGrid, you can customize the column titles. Right-click on the grid control in design-time and select Columns Editor... and a Collection window will appear. When adding a column, link it to a FieldName and then assign a value to Title.Caption. This will also require that you set up all columns. When you don't define any columns here, it automatically returns all columns in the query.
On the other hand, a SQL query may contain duplicate field names in the output, depending on how you structure the query. I know this is possible in SQL Server, but I'm not sure about MS Access. In any case, I recommend always returning a dataset with unique column names and then customizing the DB Grid's column titles. After all, it is also possible to connect to an excel spreadsheet, which can very likely have identical column names. The problem arrives when you try to read from one of those columns for another use.
I am working on a Ruby on Rails app. We are using a PostgreSQL database.
There is a table named scores with the following columns:
Column | Type
--------------+-----------------------
id | integer
value | double precision
ran_at | timestamp
active | boolean
build_id | bigint
metric_id | integer
platform_id | integer
mode_id | integer
machine_id | integer
higher_better | boolean
job_id | integer
variation_id | integer
step | character varying(255)
I need to add a sequence to job_id (note: there is no model for job).
How do I create this sequence?
Use CREATE SEQUENCE:
CREATE SEQUENCE scores_job_id_seq; -- = default name for plain a serial
Then add a column default to scores.job_id:
ALTER TABLE scores ALTER COLUMN job_id SET DEFAULT nextval('scores_job_id_seq');
If you want to bind the sequence to the column (so it is deleted when the column is deleted), also run:
ALTER SEQUENCE scores_job_id_seq OWNED BY scores.job_id;
All of this can be replaced with using the pseudo data type serial for the column job_id to begin with:
Safely and cleanly rename tables that use serial primary key columns in Postgres?
If your table already has rows, you may want to set the SEQUENCE to the next highest value and fill in missing serial values in the table:
SELECT setval('scores_job_id_seq', COALESCE(max(job_id), 1)) FROM scores;
Optionally:
UPDATE scores
SET job_id = nextval('scores_job_id_seq')
WHERE job_id IS NULL;
How to check a sequence efficiently for used and unused values in PostgreSQL
Postgres manually alter sequence
How to reset postgres' primary key sequence when it falls out of sync?
The only remaining difference, a serial column is also set to NOT NULL. You may or may not want that, too:
ALTER TABLE scores ALTER COLUMN job_id SET NOT NULL;
But you cannot just alter the type of an existing integer:
ALTER TABLE scores ALTER job_id TYPE serial;
serial is not an actual data type. It's just a notational convenience feature for CREATE TABLE.
In Postgres 10 or later consider an IDENTITY column:
Auto increment table column
So I figured out how to do this using ActiveRecord migrations on Ruby on Rails. I basically used Erwin's commands and help from this page and put them in the migration files. These are the steps:
1.
In the terminal, type:
rails g migration CreateJobIdSequence
rails g migration AddJobIdSequenceToScores
2.
Edit the migration files as follows:
20140709181616_create_job_id_sequence.rb :
class CreateJobIdSequence < ActiveRecord::Migration
def up
execute <<-SQL
CREATE SEQUENCE job_id_seq;
SQL
end
def down
execute <<-SQL
DROP SEQUENCE job_id_seq;
SQL
end
end
20140709182313_add_job_id_sequence_to_scores.rb :
class AddJobIdSequenceToScores < ActiveRecord::Migration
def up
execute <<-SQL
ALTER SEQUENCE job_id_seq OWNED BY scores.job_id;
ALTER TABLE scores ALTER COLUMN job_id SET DEFAULT nextval('job_id_seq');
SQL
end
def down
execute <<-SQL
ALTER SEQUENCE job_id_seq OWNED BY NONE;
ALTER TABLE scores ALTER COLUMN job_id SET NOT NULL;
SQL
end
end
3.
Migrate the database. In the terminal type:
rake db:migrate
I have a model for stocks and a model for stock_price_history.
I want to mass insert with this
sqlstatement = "INSERT INTO stock_histories SELECT datapoint1 AS id,
datapoint2 AS `date` ...UNION SELECT datapoint9,10,11,12,13,14,15,16,
UNION SELECT datapoint 17... etc"
ActiveRecord::Base.connection.execute sqlstatement
However, I don't actually want to use datapoint1 AS id. If I leave it blank I get an error that my model has 10 fields and I'm inserting only 9 and that it is missing the primary key.
Is there a way to force an auto increment on the id when inserting by SQL?
Edit: Bonus question cause I'm a noob. I am developing in SQLite3 and deploying to a Posgres (i.e. Heroku), Will I need to modify the above mass insert statement so it's for a posgres database?
2nd edit: my initial question had Assets and AssetHistory instead of Stocks and Stock_Histories. I changed it to Stocks / Stock price histories because I thought it was more intuitive to understand. Therefore some answers refer to Asset Histories for this reason.
You can change your SQL and be more explicit about which fields you're inserting, and leave id out of the list:
insert into asset_histories (date) select datapoint2 as `date` ...etc
Here's a long real example:
jim=# create table test1 (id serial not null, date date not null, name text not null);
NOTICE: CREATE TABLE will create implicit sequence "test1_id_seq" for serial column "test1.id"
CREATE TABLE
jim=# create table test2 (id serial not null, date date not null, name text not null);
NOTICE: CREATE TABLE will create implicit sequence "test2_id_seq" for serial column "test2.id"
CREATE TABLE
jim=# insert into test1 (date, name) values (now(), 'jim');
INSERT 0 1
jim=# insert into test1 (date, name) values (now(), 'joe');
INSERT 0 1
jim=# insert into test1 (date, name) values (now(), 'bob');
INSERT 0 1
jim=# select * from test1;
id | date | name
----+------------+------
1 | 2013-03-14 | jim
2 | 2013-03-14 | joe
3 | 2013-03-14 | bob
(3 rows)
jim=# insert into test2 (date, name) select date, name from test1 where name <> 'jim';
INSERT 0 2
jim=# select * from test2;
id | date | name
----+------------+------
1 | 2013-03-14 | joe
2 | 2013-03-14 | bob
(2 rows)
As you can see, only the selected rows were inserted, and they were assigned new id values in table test2. You'll have to be explicit about all the fields you want to insert, and ensure that the ordering of the insert and the select match.
Having said all that, you might want to look into the activerecord-import gem, which makes this sort of thing a lot more Railsy. Assuming you have a bunch of new AssetHistory objects (not persisted yet), you could insert them all with:
asset_histories = []
asset_histories << AssetHistory.new date: some_date
asset_histories << AssetHistory.new date: some_other_date
AssetHistory.import asset_histories
That will generate a single efficient insert into the table, and handle the id for you. You'll still need to query some data and construct the objects, which may not be faster than doing it all with raw SQL, but may be a better alternative if you've already got the data in Ruby objects.
For one reason or another the pre-existing Postgres schema I'm using with my Rails app doesn't have a default sequence set for a table's primary key, so I am required to query for it every time I want to create a new row.
I have set_sequence_name "seq_people_id" in my model, but whenever I call Person.new Postgres complains to me because Rails is executing the insert query without the ID (which is marked as NOT NULL in the schema).
How do I tell Rails to always use the sequence when creating new records?
Postgres 8.1.4
ActiveRecord 3.0.3
Rails 2.3.10
Here's what I get when I run psql and \d foo:
Table "public.foo"
Column | Type | Modifiers
--------+---------------+------------------------------------------------------
id | integer | not null default nextval('foo_id_seq'::regclass)
(etc.)
I'd check the following:
Verify the actual sequence name is the same as what you reference (people_id_seq vs. seq_people_id)
Verify the table's default is similar to what I have above
(just checking) is the primary key's field named "id" ?
Did you create the table using a migration or by hand? If the latter, try creating a table with a migration, specifying the same fields as in your people table. Does it work properly? Compare the tables.