I am using sqlite to store my data. I have two databases. In my application, each time a new request comes, I am attaching first db to second db. The problem is, if two request come it is showing the db already in use (it is trying to attach twice with same alias name 'db'). I want to know if there is any way to check whether a database is attached or not?
PRAGMA database_list;
outputs a resultset with full list of available databases. The first column is database name, the second is database file (empty if it is not associated with file). The primary database is always named main, temporary db is always temp.
sqlite> attach "foo.db" as foo;
sqlite> pragma database_list;
0|main|
2|foo|/Users/me/tmp/foo.db
I assume you are reusing the same connection to the database for multiple requests. Because databases are attached to the connection object, attaching fails for the second or further requests with the same connection. The solution I think is thus to attach the database immediately after a new connection is made, and not each time a request is received.
Related
I deployed my project into eb and a form submission doesn't work on eb even though it works on local. And I found the cause.
One of the attribute of a model that is not allowed to be null still remains on RDS even though I removed it in the past.
Log error is like this
ERROR: null value in column "a_variable" violates not-null constraint
How can I handle with this problem? Is there a way to remove the column manually on RDS? I am using PostgreSQL as the db engine.
Your RDS database is just a normal PostgreSQL database. If you really need to access it directly, you can:
Create a security group to open up the PostgreSQL port (5432 with TCP) to your current IP address.
Add the security group to your RDS instance (temporarily, don't forget to remove it later)
Use psql on your local machine to connect to your RDS instance, with your django credentials.
Run the normal SQL command (ALTER TABLE table_name DROP COLUMN column_name;) to delete the column. Be careful! you're directly manipulating your database.
To be sure I would check the django-migrations table to see if all migrations were run correctly. you might run into problems with later migrations if that isn't the case.
I never had to deal with database, therefore, sorry in advance!
I was asked to create a database for a project and store data output from a c++ program into the database. I informed on Google about databases, and I came across with MySQL, and in particular database connection. As far as I understood, in the first place a database has to be created (for example with MySQL), and once data are inserted, it’s possible to access to them. However, it’s not totally clear what is possible to achieve with such a connection and how to save data from a c++ program into the database directly.
Based on what I read on the net, these should be related, is it right? I would really need some help, example or clarification about these two questions. Thanks in advance for your time!
First you should create DB and tables.
You can do it in each DB IDE wizards, or you can write it in a script.
So here are scrypt for MySQL
CREATE DATABASE test_db --this create DB called test_db
I guess you should store a message and a timestamp so a possible table (In MySQL) will be:
USE test_db -- from now on the script using test_db unless specified explicit DB
--creating table with id, mmessage and timestamp
CREATE TABLE output_table (
msg_ID INT(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,
msg VARCHAR(max),
msg_TS TIMESTAMP DEFAULT CURRENT_TIMESTAMP)
In the above table you only need to give the message since all the rest are filled automatically. So Insert into the table command may look like this:
INSERT INTO output_table (msg) values ('this is a message')
When you want to check the whole table you run the following:
SELECT * FROM output_table
Now you need to connect this code to your c++ code:
Generally, you'll need to know db name, user name and password in manner to connect to DB.
You can use ODBC + MySQL ODBC Connector. It is better since you are not limitted in your c++ to a specific DB. If you are sure you will use only MySQL you can use also MySQL C++ Connector directly. Anyway, both will give you option to run SQL commands on your DB.
HERE you can fine MySQL c++ connector sample
HERE you can find ODBC sample.
How can (or, Can) I find out which iCloud database a CKRecord belongs to?
There should be four possiblities at this time:
private
public
shared
no database connection yet, if created on device
There is nothing in CKRecord that directly tells you what database it came from. But you always know the database from the source of the record.
If you get a subscription notification or from fetching changes, you know the database from the CKQueryNotification, CKRecordZoneNotification, or the new CKDatabaseNotification.
Of course if you are creating a new CKRecord, there is no database yet but you must know which database you intend to use (public, private, or the new shared).
Certainly if you get a CKRecord from performing a query, you know which database was used for the query operation.
If you need to persist a local copy of the record and then later you need to load that local copy and send it to the proper database, then your local copy must include data telling you which database it belongs to. Since you can always determine the source of a CKRecord when you obtain the record, this isn't an issue.
I'm using ColdFusion to connect to a RedShift database and I'm trying to understand how to test/assume myself of how the connections work in relation to TEMP tables in RedShift.
In my CFADMIN for the datasource I have unchecked Maintain connections across client requests. I would assume then each user who is using my website would have their own "Connection" to the DB? Is that correct?
Per the RedShift docs about temp tables:
TEMP: Keyword that creates a temporary table that is visible only within the current session. The table is automatically dropped at the end of the session in which it is created. The temporary table can have the same name as a permanent table. The temporary table is created in a separate, session-specific schema. (You cannot specify a name for this schema.) This temporary schema becomes the first schema in the search path, so the temporary table will take precedence over the permanent table unless you qualify the table name with the schema name to access the permanent table.
Am I to understand that if #1 is true and each user has their own connection to the database and thereby their own session then per #2 any tables that are created will be only in that session even though the "user" is the same as it's a connection from my server that is using the same credentials.
3.If my assumptions in #1 and #2 are correct then if I have ColdFusion code that runs a query like so:
drop if exists tablea
create temp table tablea
insert into tablea
select * from realtable inner join
drop tablea
And multiple users are using that same function that does this. They should never run into any conflicts where one table gets dropped as another request is trying to use it correct?
How do I test that this is the case? Besides throwing it into production and waiting for an error how can I know. I tried running a few windows side by side in different browsers and stuff and didn't notice an issue, but I don't know how to know if the temp tables truly are different between clients. (as they should be.) I imagine I could query some meta data but what meta data about the table would tell me that?
I have a similar situation, but with redbrick database software. I handle it by creating unique table names. The general idea is:
Create a table name something like this:
<cfset tablename = TableText & randrange(1, 100000)>
Try to create a table with that name. If you fail try again with a different name.
If you fail 3 times stop trying and mail the cfcatch information to someone.
I have all this code in a custom tag.
Edit starts here
Based on the comments, here is some more information about my situation. In CFAdmin, for the datasource being discussed, the Maintain Connections box is checked.
I put this code on a ColdFusion page:
<cfquery datasource="dw">
create temporary table dan (f1 int)
</cfquery>
I ran the page and then refreshed it. The page executed successfully the first time. When refreshed, I got this error.
Error Executing Database Query.
** ERROR ** (7501) Name defined by CREATE TEMPORARY TABLE already exists.
That's why I use unique tablenames. I don't cache the queries though. Ironically, my most frequent motivation for using temporary tables is because there are situations where they make things run faster than using the permanent tables.
I have two Django sites: one for development and one for production. Every once in a while, the data from the development database needs to be transferred to the production database or the other way around. I use postgresql.
This works fine: I empty the tables from the database I want to copy to, I generate sql from the applicable tables, and insert the data in the emptied tables. So far, so good.
But when I enter data into the database via the admin interface, Django raises IntegrityErrors, because appname_modelname_pkey already exists.
I think this is because the admin interface wants to add data with id 1, but that's already an imported record. Django isn't aware that id '1' is already taken.
How do I fix this problem? I want Django to increment the id (like SQL auto_increment would do), no matter what data is already stored.
Any help is appreciated!
If you're using postgres on both sides, then the sequence associated with the primary keys are going to be different.
For example, suppose you're moving production data to development. Also, suppose the sequence value in production is 20 and the sequence in development is 10. Then the first new item you add in development will have an id of 11. That id (probably) already exists in the production data, so you get an integrity error.
When you restore tables from a dump, you can reset the sequences by dropping and recreating the existing tables before you restore.
(Or, you can probably use the ALTER SEQUENCE command to sync up the sequences. However, I'm not familiar enough with postgres to say whether that's the right way to do it.)