8.1.2 Error Handling

When writing scripts for MySQL Shell you can often simply rely on the exception handling done by MySQL Shell. For all other languages either proper exception handling is required to catch errors or the traditional error handling pattern needs to be used if the language does not support exceptions.

The default error handling can be changed by creating a custom SessionContext and passing it to the mysqlx.getSession() function. This enables switching from exceptions to result based error checking.

The following example shows how to perform proper error handling. The example assumes that the test schema exists and that the collection my_collection exists.

MySQL Shell JavaScript Code

var mysqlx = require('mysqlx');

var mySession;

try {
  // Connect to server on localhost
  mySession = mysqlx.getSession( {
    host: 'localhost', port: 33060,
    user: 'user', password: 'password' } );
}
catch (err) {
  print('The database session could not be opened: ' + err.message);
}

try {
  var myDb = mySession.getSchema('test');

  // Use the collection 'my_collection'
  var myColl = myDb.getCollection('my_collection');

  // Find a document
  var myDoc = myColl.find('name like :param').limit(1)
    .bind('param','L%').execute();

  // Print document
  print(myDoc.first());
}
catch (err) {
  print('The following error occurred: ' + err.message);
}
finally {
  // Close the session in any case
  mySession.close();
}

MySQL Shell Python Code

from mysqlsh import mysqlx

mySession

try:
        # Connect to server on localhost
        mySession = mysqlx.get_session( {
                'host': 'localhost', 'port': 33060,
                'user': 'user', 'password': 'password' } )

except Exception as err:
        print('The database session could not be opened: %s' % str(err))

try:
        myDb = mySession.get_schema('test')

        # Use the collection 'my_collection'
        myColl = myDb.get_collection('my_collection')

        # Find a document
        myDoc = myColl.find('name like :param').limit(1).bind('param','L%').execute()

        # Print document
        print(myDoc.first())
except Exception as err:
        print('The following error occurred: %s' % str(err))
finally:
        # Close the session in any case
        mySession.close()

Node.js JavaScript Code

var mysqlx = require('@mysql/xdevapi');

// Connect to server on localhost
mysqlx
  .getSession({
    host: 'localhost',
    port: 33060,
    user: 'user',
    password: 'password'
  })
  .then(function (mySession) {
    // This can't throw an error as we check existence at a later operation only
    var myDb = mySession.getSchema('test');

    // Use the collection 'my_collection'
    // This can't throw an error as we check existence at a later operation only
    var myColl = myDb.getCollection('my_collection');

    // Find a document
    return myColl
      .find('name like :param')
      .limit(1)
      .bind('param','L%')
      .execute(function (row) {
        console.log(row);
      })
      .then(function () {
        return session.close();
      })
      .catch(function (err) {
        console.log('The following error occurred: ' + err.message);
      });
  })
  .catch (err) {
    console.log('The database session could not be opened: ' + err.message);
  });

C# Code

Session mySession = null;
try
{
  // Connect to server on localhost
  mySession = MySQLX.GetSession("mysqlx://user:password@localhost:33060");
 
  try
  {
    Schema myDb = mySession.GetSchema("test");
 
    // Use the collection 'my_collection'
    Collection myColl = myDb.GetCollection("my_collection");
 
    // Find a document
    DocResult myDoc = myColl.Find("name like :param").Limit(1).Bind("param", "L%").Execute();
 
    // Print document
    Console.WriteLine(myDoc.FetchOne());
  }
  catch (Exception err)
  {
    Console.WriteLine("The following error occurred: " + err.Message);
  }
  finally
  {
    // Close the session in any case
    mySession.Close();
  }
}
catch (Exception err)
{
  Console.WriteLine("The database session could not be opened: " + err.Message);
}

Python Code

import mysqlx

# Connect to server
my_session = mysqlx.get_session({
    'host': 'localhost', 'port': 33060,
    'user': 'user', 'password': 'password'
})

# Get the Schema test
my_schema = my_session.get_schema('test')

# Create a new collection
my_coll = my_schema.create_collection('my_collection')

# Start a transaction
my_session.start_transaction()
try:
    my_coll.add({'name': 'Rohit', 'age': 18, 'height': 1.76}).execute()
    my_coll.add({'name': 'Misaki', 'age': 24, 'height': 1.65}).execute()
    my_coll.add({'name': 'Leon', 'age': 39, 'height': 1.9}).execute()

    # Commit the transaction if everything went well
    result = my_session.commit()

    # handle warnings
    if result.get_warnings_count() > 0:
        for warning in result.get_warnings():
            print('Type [{0}] (Code {1}): {2}'.format(warning['level'], warning['code'], warning['msg']))

    print('Data inserted successfully.')
except Exception as err:
    # Rollback the transaction in case of an error
    my_session.rollback()

    # handle warnings
    if reply.get_warnings_count() > 0:
        for warning in result.get_warnings():
            print('Type [{0}] (Code {1}): {2}'.format(warning['level'], warning['code'], warning['msg']))

    # Printing the error message
    print('Data could not be inserted: {0}'.format(err))

Java Code

import com.mysql.cj.xdevapi.*;

Session mySession;

try {
    // Connect to server on localhost
    mySession = new SessionFactory().getSession("mysqlx://localhost:33060/test?user=user&password=password");

    try {
        Schema myDb = mySession.getSchema("test");

        // Use the collection 'my_collection'
        Collection myColl = myDb.getCollection("my_collection");

        // Find a document
        DocResult myDoc = myColl.find("name like :param").limit(1).bind("param", "L%").execute();

        // Print document
        System.out.println(myDoc.fetchOne());
    } catch (XDevAPIError err) { // special exception class for server errors
        System.err.println("The following error occurred: " + err.getMessage());
    } finally {
        // Close the session in any case
        mySession.close();
    }
} catch (Exception err) {
    System.err.println("The database session could not be opened: " + err.getMessage());
}

C++ Code

#include <mysqlx/xdevapi.h>

try
{
  // Connect to server on localhost
  Session session(33060, "user", "password");

  try
  {
    Schema db = session.getSchema("test");

    // Use the collection 'my_collection'
    Collection myColl = db.getCollection("my_collection");

    // Find a document
    auto myDoc = myColl.find("name like :param").limit(1)
                       .bind("param", "L%").execute();

    // Print document
    cout << myDoc.fetchOne() << endl;

    // Exit with success code
    exit(0);
  }
  catch (const Error &err)
  {
    cout << "The following error occurred: " << err << endl;
    exit(1);
  }

  // Note: session is closed automatically when session object
  // is destructed.
}
catch (const Error &err)
{
  cout << "The database session could not be opened: " << err << endl;

  // Exit with error code
  exit(1);
}