I am using sqlite c/c++ interface.
I have 3 tables (related tables) say A, B, C. Now, there is a function called Set, which get some inputs and based on the inputs inserts rows into these three tables. (sometimes it can be an update in one of the tables)
Now I need two things. One, i dont want autocommit feature. Basically I would like to commit after every 1000 calls to Set function
Secondly, within the set function itself, if i find that after inserting into two tables, the third insert fails, then i have to revert, those particular changes in that Set function call.
Now i don't see any sqlite3_commit function exposed. I only see a function called sqlite3_commit_hook() which is slightly diff in documentation.
Are there any function exposed for this purpose? or What is the way to achieve this behaviour?
Can you help me with the best approach of doing this.
You use sqlite3_exec and pass "BEGIN TRANSACTION" and "END TRANSACTION" respectively.
// 'db' is the pointer you got from sqlite3_open*
sqlite3_exec(db, "BEGIN TRANSACTION;", NULL, NULL, NULL);
// Any (modifying) SQL commands executed here are not committed until at the you call:
sqlite3_exec(db, "END TRANSACTION;", NULL, NULL, NULL);
There are synonyms for these SQL commands (like COMMIT instead of END TRANSACTION). For reference, here is the SQLite documentation for transactions.
Related
I am attempting to use OTL to do a basic insert into a sql server db. For this insert I don't need to bind any parameters.
otl_stream o_stream;
std::string query = "INSERT INTO common VALUES (1,2,3);";
o_stream.open(1, query.c_str(), db_);
o_stream.flush();
o_stream.close();
However, even after flushing and closing the otl_stream, the db is locked on that table (can't read via separate application). I have to close my otl application to unlock the table.
If I parameterize the insert statement then everything works as it should (inserts successful, no table lock).
otl_stream o_stream;
std::string query = "INSERT INTO common VALUES (1,2,a:<int>);";
o_stream.open(1, query.c_str(), db_);
o_stream << 3;
That's not ideal, since ideally I'd like to avoid parameterizing/binding if it's not necessary.
Any suggestions?
EDIT:
Answer Below
From the author of the OTL library:
otl_streams are meant to be reused, that is, a INSERT statement stream
needs to have at least one bind variable to be "flushable". For cases
when there is 0 bind variables, there is this:
http://otl.sourceforge.net/otl3_const_sql.htm.
Missing from that link is the required db.commit() call. Without the commit call the table will be locked.
Solution for the example given in the question:
std::string query = "INSERT INTO common VALUES (1,2,3);";
db_.direct_exec(query.c_str());
db_.commit();
Consider following code and advise, why can I not address the temporary table created in the current session.
CDatabase cdb;
CString csConnectionString = "Dsn=prm2;Driver={INFORMIX 3.34 32 BIT};Host=10.XXX.XXX.XXX;Server=SRVNAME;Service=turbo;Protocol=olsoctcp;Database=DBNAME;Uid=user;Pwd=password";
cdb.OpenEx(csConnectionString, CDatabase::noOdbcDialog);
cdb.ExecuteSQL(CString("Set Isolation to Dirty Read"));
...
CString csStatement1 = "SELECT serno FROM TABLE1 into temp ttt_1;"
CString csStatement2 = "DROP TABLE ttt_1";
cdb.ExecuteSQL(csStatement1); // point1
cdb.ExecuteSQL(csStatement2); // point2
...
cdb.Close();
At point1 everything is fine. At point2 I have:
The specified table (ttt_1) is not in the database. State:S0002,Native:-206,Origin:[Informix][Informix ODBC Driver][Informix]
I tried to specify username as prefix (like user.ttt_1 or "user".ttt_1); I tried to create permanent table within respective statement in csStatement1 and every time it failed at point2. But when I tried to create same temporary table twice within csStatement1 I got the message that the temporary table already exists in session.
Please advise: what is wrong and how can I address created temporary tables.
it is all to do with ODBC autocommit mode. By default ODBC uses the option what is defined during the connection, and according to connectionstrings.com the default settings for Informix is commitretain=false.
You have two options: either set it via the connection string (commitretain=true) or (better option) via the ODBC. For a set of statements where you'd like to retain the temp table activate the manual commit mode via SqlSetConnectAttr, then execute a few statements and then call SqlEndTran. Please note, that in manual mode you do not need to call BEGIN TRANSACTION, as it will start automatically (behaviour similar to Oracle)
Please note that ODBC applications should not use Transact-SQL transaction statements such as BEGIN TRANSACTION, COMMIT TRANSACTION, or ROLLBACK TRANSACTION, but use the ODBC commands.
It seems that c++ drivers doesn't accept mongodb connection uri format.
There's no documentation on how i should create connection string, any guess?
I need to connect to a replica set with 3 servers, and set readPreference options.
Create a connection to a replica set in MongoDB C++ client
Until the problems explained in #acm's answer are resolved, I have found a workaround to the bad Connection Strings of the C++ driver. You can create a DBClientReplicaSet using a vector of hosts and ports this way:
//First create a vector of hosts
//( you can ignore port numbers if yours are default)
vector<HostAndPort> hosts;
hosts.push_back(mongo::HostAndPort("YourHost1.com:portNumber1"));
hosts.push_back(mongo::HostAndPort("YourHost2.com:portNumber2"));
hosts.push_back(mongo::HostAndPort("YourHost3.com:portNumber3"));
//Then create a Replica Set DB Client:
mongo::DBClientReplicaSet connection("YourReplicaSetName",hosts,0);
//Connect to it now:
connection.connect();
//Authenticate to the database(s) if needed
std::string errmsg;
connection.auth("DB1Name","UserForDB1","pass1",errmsg);
connection.auth("DB2Name","UserForDB2","pass2",errmsg);
Now, you can use insert, update, etc. just as you did with DBClientConnection. For a quick fix, you can replace your references to DBClientConnection with DBClientBase (which is a parent to both DBClientConnection and DBClientReplicaSet)
Last pitfall: if you are using getLastError(), you must use it with the aimed database name like this:
connection.getLastError(std::string("DBName"));
cause otherwise it will always return "command failed: must log in" as described in this JIRA ticket.
Set the read preferences for every request
You have two ways to do that:
SlaveOK option
It lets your read queries be directed to secondary servers.
It takes place in the query options, which are at the end of the parameters of DBClientReplicaSet.query(). The options are listed in Mongo's official documentation
The one you would look for is mongo::QueryOption_SlaveOk, which will allow you to have reads made on secondary instances.
This is how you should call query();
connection.query("Database.Collection",
QUERY("_id" << id),
n,
m,
BSON("SomeField" << 1),
QueryOption_SlaveOk);
where n is the number of documents to return (0 if you don't want any limit), m the number to skip (defaults to 0), the next field is your projection and the last your query option.
To use several query option, you can use bitwise or | like this :
connection.query("Database.Collection",
QUERY("_id" << id),
n,
m,
BSON("SomeField" << 1),
QueryOption_SlaveOk | QueryOption_NoCursorTimeout | QueryOption_Exhaust);
Query::readPref option
The Query object has a readPref method which sets read preferences for a special query. It should be called for each query.
You can pass different arguments for more control. They are listed here.
So here's what you should do (I did not test that one cause I can't right now but it should work just fine)
/* you should pass an array for the tags. Not sure if this is required.
Anyway, let's create an empty array using the builder. */
BSONArrayBuilder bab;
/* if any, add your tags here */
connection.query("Database.Collection",
QUERY("_id" << id).readPref(ReadPreference_SecondaryPreferred, bab.arr()),
n,
m,
BSON("SomeField" << 1),
QueryOption_NoCursorTimeout | QueryOption_Exhaust);
Note: if any readPref option is used, it should override the slaveOk option.
Hope this helped.
Please see the connection string documentation for details on the connection string format.
(code links below are to 2.2.3 files)
To use a connection string with the C++ driver, you should use the ConnectionString class. You first call the ConnectionString::parse static method with a connection string to obtain a ConnectionString object. You then call ConnectionString::connect to obtain a DBClientBase object which you can then use to send queries.
As for read preference, at the moment I do not see a way to set the read preference in the connection string for the C++ driver, which would preclude a per-connection setting.
However, the implementation of DBClientBase returned by calling ConnectionString::parse with a string that identifies a replica set will return you an instance of DBClientReplicaSet. That class honors $readPreference in queries, so you can set your read preference on a per-query basis.
Since the current C++ drivers still do not accept the standard mongodb connection URIs, I've opened a ticket:
https://jira.mongodb.org/browse/CXX-2
Please vote for it to help get this fixed.
it seems like you can set read Preference before send a read request by call "readPref" method of your Query object. I'v not found a way to set read Preference on mongo collection object yet.
Is it possible to set a connection parameter on a connection to SQL Server and have that variable persist throughout the life of the connection? The parameter must be usable by subsequent queries.
We have some old Access reports that use a handful of VBScript functions in the SQL queries (let's call them GetStartDate and GetEndDate) that return global variables. Our application would set these before invoking the query and then the queries can return information between date ranges specified in our application.
We are looking at changing to a ReportViewer control running in local mode, but I don't see any convenient way to use these custom functions in straight T-SQL.
I have two concept solutions (not tested yet), but I would like to know if there is a better way. Below is some pseudo code.
Set all variables before running Recordset.OpenForward
Connection->Execute("SET #GetStartDate = ...");
Connection->Execute("SET #GetEndDate = ...");
// Repeat for all parameters
Will these variables persist to later calls of Recordset->OpenForward? Can anything reset the variables aside from another SET/SELECT #variable statement?
Create an ADOCommand "factory" that automatically adds parameters to each ADOCommand object I will use to execute SQL
// Command has been previously been created
ADOParameter *Parameter1 = Command->CreateParameter("GetStartDate");
ADOParameter *Parameter2 = Command->CreateParameter("GetEndDate");
// Set values and attach etc...
What I would like to know if there is something like:
Connection->SetParameter("GetStartDate", "20090101");
Connection->SetParameter("GetEndDate", 20100101");
And these will persist for the lifetime of the connection, and the SQL can do something like #GetStartDate to access them. This may be exactly solution #1, if the variables persist throughout the lifetime of the connection.
Since no one has ventured an answer I'm guessing there isn't an elegant solution, that said:
Global cursors persist for the duration of the connection and can be accessed from any SQL or stored proc so you could execute this once on the connection:
DECLARE KludgeKursor CURSOR GLOBAL STATIC FOR
SELECT StartDate = '2010-01-01', EndDate = '2010-04-30'
OPEN KludgeKursor
and in your stored procedures:
--get the values
DECLARE #StartDate datetime, #EndDate datetime
FETCH FIRST FROM GLOBAL KludgeKursor
INTO #StartDate, #EndDate
--go crazy
SELECT #StartDate, #EndDate
Each connection would only see their own values, so the same stored procs can be used for different connection/values. The global cursor is automatically deallocated when the connection ends
I have a C++ application that uses ADO to talk to an Oracle database. I'm updating the application to support an offline documents. I've decided to implement SQLite for the local side.
I've implemented a wrapper around the ADO classes that will call the appropriate code. However, ADO's way of adding/editing/deleting rows is a bit difficult to implement for SQLite.
For ADO I'd write something like:
CADODatabase db;
CADORecordset rs( &db );
db.Open( "connection string" );
rs.Open( "select * from table1 where table1key=123" );
if (!rs.IsEOF())
{
int value;
rs.GetFieldValue( "field", value );
if (value == 456)
{
rs.Edit();
rs.SetFieldValue( "field", 456 );
rs.Update();
}
}
rs.Close();
db.Close();
For this simple example I realize that I could have just issued an update, but the real code is considerable more complex.
How would I get calls between the Edit() and Update() to actually update the data? My first thought is to have the Edit() construct a separate query and the Update() actually run it, but I'm not sure what fields will be changed nor what keys from the table to limit an update query to.
" but I'm not sure what fields will be changed nor what keys from the table to limit an update query to."
How about just selecting ROWID with the rest of the fields and then building an update based on that ?