Could someone please explain how to obtain a list of all existing databases on a PostgreSQL server, to which the user already has access, using Qt? PostgreSQL documentation suggests the following query:
SELECT datname FROM pg_database WHERE datistemplate = false;
What are the correct parameters to the following functions:
QSqlDatabase::setDatabaseName(const QString & name) //"postgres" or "pg_database"?
QSqlDatabase::setUserName(const QString & name) //actual user name?
QSqlDatabase::setPassword(const QString & password) //no password? or user password?
Much appreciated. Thank you in advance.
You appear to have already answered the first part of your question. Connect to the postgres or template1 database and issue the query you've quoted above to get a list of databases. I'm guessing - reading between the lines - that you don't know how to connect to PostgreSQL to send that query, and that's what the second part of your question is about. Right?
If so, the QSqlDatabase accessor functions you've mentioned are used to set connection parameters, so the "correct" values depend on your environment.
If you want to issue the query above - to list databases - then you would probably want to connect to the postgres database as it always exists and isn't generally used for anything specific, it's there just to be connected to. That means you'd call setDatabaseName("postgres");. Passing pg_database to setDatabaseName would be nonsensical, since pg_database is the pg_catalog.pg_database table, it isn't a database you can connect to. pg_database is one of those odd tables that exists in every database, which might be what confused you.
With the other two accessors specify the appropriate username and password for your environment, same as you'd use for psql; there's no possible way I could tell you which ones to use.
Note that if you set a password but one isn't required because authentication is done over unix socket ident, trust, or other non-password scheme the password will be ignored.
If this doesn't cover your question, consider editing it and explaining your problem in more detail. What've you tried? What didn't work how you expected? Error messages? Qt version?
Related
I'm referring to SQLite-PCL tutorial here: https://code.tutsplus.com/tutorials/an-introduction-to-xamarinforms-and-sqlite--cms-23020
I'm very new to SQLite, so I'm lacking in knowledge in lots of basic things - I have tried Googling, can't understand most of it.
Is the call to new SQLiteConnection actually opens up the database or just saying that "the road to the database has been established, whether you access it or not is up to you"?
How do I check if there's already existing database in the devices? And if there is, how do I access it? I have Googled this, but it all seems to be a bit extreme - can't I just call simple OPEN the database?
Is it okay to have multiple SQLiteConnection instances to the same database, if I can be sure that I'm not going to do multiple transaction at the same time?
After I have INSERT into the database, close the app, open up the app back - how do I make sure that there is database created in previous session? Any way to debug this? Because I have no idea if the database is there or not, and I don't know how to access it either..
SQLiteConnection returns a connection object that is used to make subsequent queries
use File.Exists to see if the db file is already present
Yes
Again, use File exists to see if the db file is physically present
Xamarin's ToDo sample provides a good overview of using SQLite with Forms.
I have been searching for an answer on MS, SE and Google and cannot find it. I want to use the GRS option for Azure Storage (Cloud Block Blobs) but I cannot figure out how to properly do that.
I created my storage object in Azure and chose the GRS option.
I get that I have a primary and secondary connection string and know how to get that from the Azure portal.
What I do not know, in ASP.NET 4.0, is how to set both connection strings in the CloudBlockClient and gracefully handle the primary storage being unavailable.
--What exception is thrown and where, when primary is unavailable? Is this thrown when I create the client, or when I try to get a blob reference?
-- How do I then use the secondary?
Do I have to just test for any old exception and then try using the secondary connection string in a new CloudBlockClient if the primary does not work? Or is there anything in the API for this. I would think there would be but I cannot find it.
None of the "How to use Azure Storage" tutorials I have seen go into this. Most of the documentation seems to date from before mid-2014 when this feature became generally available.
This blog post should help you. In short if you want to read from both primary and secondary you want to enable RA-GRS - essentially read access from the secondary. If you are using out storage client libraries you can also enable a retry policy that will first try to read from a primary and then from the secondary if the first read fails.
I am connecting to a Teradata database through ODBC with Stata on an Ubuntu server (12.04 LTS). Everything works fine, except that I have my TD userid and password stored in the .odbc.ini file, which seems like a terrible idea. The alternative is to enter them in Stata, which seems even worse and is awkward. Is there a way to do this more securely? The login info that I use to ssh into the server is synced with the TD database. It seems that it should be possible to pass that information along.
In ODBC terms you do not need to store usernames / passwords in any of your ODBC ini files. Both the ODBC SQLConnect and SQLDriverConnect support the passing in of username / password at the time they are called.
SQLDriverConnect would need something in your InConnectionString like "DSN=YourDataSourceName;UID=username;PWD=password".
You could go one step further and pass in the whole DSN as a command line argument thus meaning that you would not need an ODBC data source in an ini file. I'm sure one of the forum readers can post a sample for you from Teradata.
As for passing in the user name and password from your SSH loging. Your application would need to capture that and pass it to ODBC.
If you want to establish a finer grain of security around your odbc.ini file or other files on your Ubuntu server that may contain user credentials I would strongly suggest the use of Access Control Lists (ACLs). Beyond the typical Owner::Group::World permissions you can specify permissions down to the specific user on whether they are allowed or denied an explicit permission for a given file.
Other options regarding security on Teradata include the use of LDAP authentication if your environment supports it. Configuring LDAP on Teradata is beyond the scope of SO and in many cases a billable, professional services engagement with Teradata's Information Security CoE.
We have our application developed and tested with sql server 2008r2 using ASP.NET on windows server. Now we have a requirement to move the database from windows to oracle on red hat linux.
We haven't yet setup the infrastructure to test the same. I would like to know in the meantime if anyone has successfully done this kind of thing. Pointers to any resources will be a great advantage.
Is changing the connection string the only thing that needs to be done or are there any specific configuration in Linux to allow this?
I will verify this once I get the environment ready, but as a headstart if anyone has any similar experience, do share.
Thanks in advance.
P.S: For migration of table structure, storedprocedures etc to oracle we will be using the Sql Developer tool.
I would like to answer my question,because, migration to oracle is not that straight forward, but there are some tips that may help anyone migrate to oracle on windows or linux with less headache.
The first thing the Sql developer tool does a good job of migrating sqlserver schema and data to oracle including storedprocedures, constraints, triggers etc.
It also does a good job of datatype mapping and provides option to remap datatype if required.
Some caveats and precautions.
Oracle has a limitation on the length of stored procedure names of about 30 characters. This is the area you need to resort to some manual renaming as when migration SP's or identifiers whose name is greater than 30 characters may get truncated.
The other common issue that you may face is respect to date insertion and formatting. You can use the following snippet to avoid the headache. The common error will be "Not a valid month."
OracleConnection conn = new OracleConnection(oradb); // C#
conn.Open();
OracleGlobalization session = conn.GetSessionInfo();
session.DateFormat = "DD.MM.RR"; // change the format as required here
conn.SetSessionInfo(session);
The most annoying error would be well character to numeric conversion when inserting or updating data or related error.
The issue here is when you add parameters to command object for sql provider, the binding happens by name, but forOracle.DataAccess the default binding is by position. Here's the post that saved me lot of headache.
ODP .NET Parameter problem with uint datatype
What you can do is set the command.BindByName = true;
When migrating SP's that returns data, oracle creates an out parameter ref cursor. This needs to be taken care of while constructing command parameters.
For e.g.
OracleParameter refp = new Oracle.DataAccess.Client.OracleParameter("cv_1", OracleDbType.RefCursor, ParameterDirection.InputOutput);
command.Parameters.Add(refp);
Also the sqlserver requires parameters to SP be prefixed with "#" and oracle doesn't. This can be easily taken care of in your data layer.
Also since there is no bit datatype in Oracle, number(1) works fine. You may need to convert your bool to numeric, if required.
Hope this helps someone avoid a migration headaches. I will post more issues if I encounter.
Database i am using is MySQL 5.1. I specified, i believe, right connectionstring in my web.config. but when i run my web app. it throws this exception:-
MySql.Data.MySqlClient.MySqlException: The user specified as a definer ('root'#'%') does not exist
Any help. Why am i getting this?
The source code for the stored procedures that you have been loading probably contain "DEFINER=root#'%'" as part of the definition - looking a bit like this:
create definer='root'#'%' procedure sp_test() begin end;
The problem here is that you do not have an account on your system for 'root'#'%'. This can be easily demonstrated. From the MySQL command line:
show grants for 'root'#'%';
I expect that this will come back with an error message:
ERROR 1141 (42000): There is no such grant defined for user 'root' on host '%'
The fix is to alter the source of your stored procedures, or to create the missing account:
grant all on *.* to 'root'#'%' identified by 'password' with grant option;
It is not generally a good idea to have such a high-powered account accessible from anywhere, but that is another story.
I know this answer comes very late, but I found a solution that doesn't involve changing any rights at all.
Go into your Stored Procedures and delete the DEFINER clause. The server should write in a new DEFINER that matches the user information you're logged in with.
Worked for me...
Is this in a stored procedure? Then maybe this blog post helps (emphasis mine).
All the settings were fine and I was wondering what’s causing the problem. At first rush I thought that it could be a cache, as I had requested recently to have xcache on our server.
But it wasn’t the case. The error was much more stupid than even one can imagine. That specific script uses a stored procedure to insert / fetch data to/from MySQL. The user who had created the sp was the one who was deleted. And that was the problem. The term “Definer” in terms of MySQL is the one who creates the stored procedure and for the stored procedure to be executed that user must exists.