The code in my project now:
local lsqlite3 = require "lsqlite3complete"
self.db_conn = lsqlite3.open("cost.db")
function showrow(udata,cols,values,names)
assert(udata=='test_udata')
for i=1,cols do
print('',names[i],values[i])
end
return 0
end
self.db_conn:exec('select * from cost',showrow,'test_udata')
It is no problem to select the cost records from the code above, but if I change like below and try to open it in memory:
self.db_conn = lsqlite3.open_memory("cost.db")
The code has no error but there is no records or tables inside when I do the query. How can I change my code so that I can open and put my database inside memory? Since I would like to access my data quickly in memory instead of keep connecting to a database.
A memory database is one that exists only in memory. That is, it doesn't get its data from a file. Because of that, open_memory doesn't take any parameters.
If you want to use a database that lives in a file, then that means accessing that file.
You should not need to "keep connecting to a database". You connect to it once at the beginning of the application and keep it open until your application terminates.
Related
I need help in creating logs in a stored procedure.
Scenario is like:
I am creating a procedure. I need to log some intermediate information from the procedure in a log file, such that each time the procedure is executed the logs are generated.
Normally i was using SPOOL for this purpose, but as SPOOL is SQL PLUS and cannot be used in PL/SQL, i was look for a better way through which logs written to specific file each time the procedure is triggered informing the updates which are made in the procedure.
Can someone please help me in identifying any such code snap which i can insert in the stored procedure in order to meet my requirement.
NOTE: I am using Oracle.
You could simply create a package with simple logging functionality, which opens, writes and closes a log file that is stored on the database server. Look into the UTL_FILE package;
Several approaches:
Use SQL Bulk Import Stored Proc and call the stored proc with the file path
Use SqlBulkCopy in System.Data.SqlClient dll
Read the file line by line and then insert into a table row by row
Any other ways?
Which one is best? I just want the user to select a file from asp.net webpage. And then click on Upload button to store the file in DB.
Secondly, do I need to move the file in server's memory before the file is copied into db table?
The DB won't know of the file because everything should be decoupled and layered. Saving the file to some shared location adds overhead and tidy ups etc
Yes
Surely you want this to be an atomic operation. 10k rows would be 10 round trips with a client side transaction running. If not atomic, then you'd need staging tables and tidy ups
Parse in c#, send to the DB with a table valued parameter. Otherwise, probably nothing same and/or realistic...
I am completely new to SQLite and I intend to use it in a M2M / client-server environment where a database is generated on the server, sent to the client as a file and used on the client for data lookup.
The question is: can I replace the whole database file while the client is using it at the same time?
The question may sound silly but the client is a Linux thin client and to replace the database file a temporary file would be renamed to the final file name. In Linux, a program which has still open the older version of the file will still access the older data since the old file is preserved by the OS until all file handles have been closed. Only new open()s will access the new version of the file.
So, in short:
client randomly accesses the SQLite database
a new version of the database is received from the server and written to a temporary file
the temporary file is renamed to the SQLite database file
I know it is a very specific question, but maybe someone can tell me if this would be a problem for SQLite or if there are similar methods to replace a database while the client is running. I do not want to send a bunch of SQL statements from the server to the client to update the database.
No, you cannot just replace an open SQLite3 DB file. SQLite will keep using the same file descriptor (or handle in Windows-speak), unless you close and re-open your database. More specifically:
Deleting and replacing an open file is either useless (Linux) or impossible (Windows). SQLite will never get to see the contents of the new file at all.
Overwriting an SQLite3 DB file is a recipe for data corruption. From the SQLite3 documentation:
Likewise, if a rogue process opens a
database file or journal and writes
malformed data into the middle of it,
then the database will become corrupt.
Arbitrarily overwriting the contents of the DB file can cause a whole pile of issues:
If you are very lucky it will just cause DB errors, forcing you to reopen the database anyway.
Depending on how you use the data, your application might just crash and burn.
Your application may try to apply an existing journal on the new file. Sounds painful? It is!
If you are really unlucky, the user will just get back invalid results from any queries.
The best way to deal with this would be a proper client-server implementation where the client DB file is updated from data coming from the server. In the long run that would allow for far more flexibility, while also reducing the bandwidth requirements by sending updates, rather than the whole file.
If that is not possible, you should update the client DB file in three discrete steps:
Send a message to the client application to close the DB. This allows the application to commit any changes, remove any journal files and clean-up its internal state.
Replace/Overwrite the file.
Send a message to the client application to re-open the DB. You would have to setup all prepared statements again, though.
If you do not want to close the DB file for some reason, then you should have your application - or even a separate process - update the original DB file using the new file as input. The SQLite3 backup API might be of interest to you in that case.
i'm working with IronPython 2.6 for .Net4 and sqlite3 module from: IronPython.SQLite.
i have a written a GUI program what runs in four frames of an MDI window. Every of the four programs receives data from a serialport and stores this data in a sqlite database. One database per program.
Between inserting this data on receive into the database the program querys the database every 100ms for the latest data items.
I'm already using a mutex call for the cursor.execute() command to prevent problems with simultaneous commands (insert or select).
During runtime the program (sporadically) runs into an exception.
When trying to query data:
System.Exception: database disk image is malformed
or when trying to insert data:
System.Exception: database or disk is full
Is it possible, that an database query short after an database insert (or the way around) could cause such exceptions and destroy the database?
It would be very kind of you, if you could give me a kind of advice how to solve this issue.
In normal condition, I can add schemas in the dbml file to empty database with code below.
But now when I run this code, I take the error "Cannot drop database "test" because it is currently in use." How can I do it?
Dim db As New UI_Class.UIData
If db.DatabaseExists Then
db.DeleteDatabase()
End If
db.CreateDatabase()
It might happen as your SQL Server Management Studio (SSMS) must be holding it.
Most likely something is connected to the db.
Common causes are:
Some other tool connected
Trying to delete the database you connected to.
Another user connected to the db.