Question

I currently have a transaction that attempts to insert data into a table. If the data is already in the table a constraint failed error is raised and a select is run to get the ID.

t2.executeSql('INSERT INTO books (book) VALUES (?);',
  [record],
  function (t2, r) {        // SQL_successfulCallback
    record = r.insertId;
  },
  function (t2, err) {      // SQL_errorCallback
    if (err.message !== 'constraint failed') { // insert failed because of other
                                               // reason - fail transaction
      console.log('Insert SQL error ' + err.code + ' - ' + err.message + '.');
      return true;
    } else { // insert failed because data was already in the table
      t2.executeSql('SELECT bookID FROM books WHERE book=?',
        [record],
        function (t, r) {   // SQL_successfulCallback
          record = r.rows.item(0).classificationID;
        },
        function (t, err) { // SQL_errorCallback
          console.log('Lookup SQL error ' + err.code + ' - ' + err.message + '.');
          return true;
        }
      );
      return false;
    }
  }
);

I want to speed the transaction up so I thought I would see if the data was in the table first. If it isn’t then insert it…

t2.executeSql('SELECT bookID FROM books WHERE book=?',
  [record],
  function (t2, r) {          // SQL_successfulCallback
    if (r.rows.length !== 0) {
      record = r.rows.item(0).bookID;
    } else {
      t2.executeSql('INSERT INTO books (book) VALUES (?);',
        [record],
        function(t2, r){      // SQL_successfulCallbac
          record = r.insertId;
        },
        function (t2, err) {  // SQL_errorCallback
          if (err.message !== 'constraint failed') { // insert failed because of other
                                                     // reason - fail transaction
            console.log('Insert SQL error ' + err.code + ' - ' + err.message + '.');
            return true;
          } else { // insert failed because data was already in the table
            return false;
          }
        }
      );
    }
  },
  function (t, err) {         // SQL_errorCallback
    console.log('Lookup SQL error ' + err.code + ' - ' + err.message + '.');
    return true;
  }
);

…but it doesn’t work. This transaction runs all the selects then does the inserts. How can I make the second method work?

Answer 1

I’m assuming the transaction is queuing the request. So your queue will look like this

Select 1

Select 2

Select 3

Then when you commit your transaction looks like this after the first call.

Select 2

Select 3

Insert 1

Insert 2

Insert 3

This is happening because the the functions to call the inserts are exected after the select is ran and this doesn’t happen until the transaction commits but the selects have already be registered.

In order to get it to be

select1

insert1

select2

insert2

I would create a separate transaction for each select statement.