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LoggingHandler<DataObj, ParamObj>

dtl

LoggingHandler<DataObj, ParamObj>

Description

A LoggingHandler is an IOHandler function object that is called when exceptions are thrown in DB_iterator operations. This handler simply logs the exceptions that are passed to it and tells the caller to suppress the error (dtl_ios_base::SUPPRESS_ERROR). AlwaysThrowsHandler is the default handler for a DBView.

Definition

Defined in the DBView.h header file.

Associated types

AlwaysThrowsHandler, BulkFetchHandler, IOHandler.

The following nested struct is defined.:

// log entry describing exception information including stringified exception and relevant DataObj and ParamObj

struct LoggedTriple

{

    string errmsg; // message describing the exception thrown - usually the stringified exception

    DataObj dataObj; // DataObj relevant to the exception thrown

    ParamObj paramObj; // ParamObj relevant to the exception thrown


    LoggedTriple() : errmsg(""), dataObj(), paramObj() { }


    LoggedTriple(const string &msg, const DataObj &data, const ParamObj &param) :

      errmsg(msg), dataObj(data), paramObj(param) { }

};

Example:

// Example Code Using LoggingHandler on a DBView


// test of failed SelValidate() when reading data

void TestBadSelValidate()

{

     vector<Example> results;


    // construct view

    // DBView<Example> is actually DBView<Example, 

    // DefaultParamObj<Example> > thanks to the default 

    // argument to the DBView template


    // use our bad BCA which references a nonexistent column name in DB_EXAMPLE

    DBView<Example>
        view("DB_EXAMPLE", BCAExampleObj(),

        "WHERE INT_VALUE BETWEEN (?) AND (?) AND "
        "STRING_VALUE = (?) OR EXAMPLE_DATE < (?) ORDER BY EXAMPLE_LONG",

        BPAExampleObj(), BadSelValidate());


    view.set_io_handler(LoggingHandler<Example>());


    // loop through query results and add them to our vector

    // in this loop, read_it.GetLastCount() records read from DB


    DBView<Example>::select_iterator read_it = view.begin();


    // set parameter values for the WHERE clause in our SQL query

    read_it.Params().lowIntValue = 2;

    read_it.Params().highIntValue = 8;

    read_it.Params().strValue = "Example";
    

    TIMESTAMP_STRUCT paramDate = {2000, 1, 1, 0, 0, 0, 0};

    read_it.Params().dateValue = paramDate;


    for ( ; read_it != view.end(); read_it++)

    {

        try

        {

          // note that the read_iterator::GetLastCount()  is incremented in operator++()

          // remember that the record is fetched and thus the count incremented

          // before operator*() is applied to the read_iterator


          cout << "Reading element #" << read_it.GetLastCount() << endl;
          

          cout << "read_it->exampleInt = " << read_it->exampleInt << endl;

          cout << "read_it->exampleStr = " << read_it->exampleStr << endl;
          

          results.push_back(*read_it);

        }

        catch (RootException &ex)

        {

          cout << "Caught Exception!!!!" << endl;

          cout << ex.what() << endl;

        }

    }


    LoggingHandler<Example> handler = 

        read_it.get_io_handler((LoggingHandler<Example> *) NULL);


    typedef LoggingHandler<Example>::LoggedTriple LoggedTriple;


    vector<LoggedTriple> errors = handler.GetLog();


    for (vector<LoggedTriple>::iterator log_it = errors.begin(); log_it != errors.end();

            log_it++)

    {

        LoggedTriple error = *log_it;


        cout << "Error msg = " << error.errmsg << endl;

        cout << "Example = " << error.dataObj << endl;

    }


}

// Example Code Using LoggingHandler on an IndexedDBView


const TIMESTAMP_STRUCT then = {2000, 12, 15, 0, 0, 0, 0};


// Example of using an IndexDBView to try to insert Example objects and print out

// any errors that occurred

void IndexedViewExample()

{

    typedef DBView<Example, ParamObjExample> DBV;


    DBV view("DB_EXAMPLE", DefaultBCA<Example>(), 

      "WHERE INT_VALUE BETWEEN (?) AND (?) OR "
      "STRING_VALUE = (?) OR EXAMPLE_DATE <= (?) ORDER BY EXAMPLE_LONG",

      BPAExampleObj());


    view.set_io_handler(LoggingHandler<Example, ParamObjExample>());


    IndexedDBView<DBV> indexed_view(view, "PrimaryIndex; STRING_VALUE; UNIQUE AlternateIndex; EXAMPLE_LONG, 

        EXAMPLE_DATE", BOUND, USE_ALL_FIELDS, cb_ptr_fun(SetParamsExample));


    try

    {


    // Insert new items into the container

    pair<IndexedDBView<DBV>::iterator, bool> ins_pr;


    ins_pr = indexed_view.insert(Example(459, "Unique String #1", 3.4, 1, date_criteria));


    cout << "insertion succeded = " << (ins_pr.second == true ? "true": "false") << endl;


    ins_pr = indexed_view.insert(Example(311, "", 3.99, 91, then)); // should fail on InsValidate()
   

    cout << "insertion succeded = " << (ins_pr.second == true ? "true": "false") << endl;
    

    ins_pr = indexed_view.insert(Example(222, "Positron", -34.77, 29, then)); // should fail (ditto)
    

    cout << "insertion succeded = " << (ins_pr.second == true ? "true": "false") << endl;

    }
    

    catch (...)

    {

    typedef LoggingHandler<Example, ParamObjExample>::LoggedTriple LoggedTriple;
 

    // retrieve the LoggingHandler object from the IndexedDBView

    LoggingHandler<Example, ParamObjExample> log_handler = 

        indexed_view.get_io_handler((LoggingHandler<Example, ParamObjExample> *) NULL);


    // the log is a vector of (error message, DataObj, ParamObj) triples,

    // (error message, Example object, ParamObjExample object) in this case

    // the error itself along with the relevant DataObj and ParamObj that resulted with

    // the error

    vector<LoggedTriple> error_log = log_handler.GetLog();


    // nothing to do if no errors occurred

    if (error_log.empty())

        return;


    cout << "*** Error Log in IndexedViewExample(): " << error_log.size() << " errors recorded! ***"
         << endl;


    // print out the errors

    for (vector<LoggedTriple>::const_iterator log_it = error_log.begin(); 

        log_it != error_log.end(); log_it++)

    {

       cout << "*** Error Log Entry ***" << endl;

       cout << "* error message *" << endl;

       cout << (*log_it).errmsg << endl;

       cout << "* relevant Example object *" << endl;

       cout << (*log_it).dataObj << endl;

    }


    }	

}

Public Base Classes

None.

Template parameters

Notation

Expression semantics

See also

AlwaysThrowsHandler, BulkFetchHandler, IOHandler, DBView, IndexedDBView

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Copyright � 2002, Michael Gradman and Corwin Joy.

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