ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Working with local SQL databases in AIR
As a general rule, any object that you store in a database using an INSERT statement is returned as an instance of the
same data type when you execute a SELECT statement. However, the data type of the retrieved value can be different
depending on the affinity of the database column in which the value is stored. When a value is stored in a column, if
its data type doesn’t match the column’s affinity, the database attempts to convert the value to match the column’s
affinity. For example, if a database column is declared with NUMERIC affinity, the database attempts to convert inserted
data into a numeric storage class (INTEGER or REAL) before storing the data. The database throws an error if the data
can’t be converted. According to this rule, if the String “12345” is inserted into a NUMERIC column, the database
automatically converts it to the integer value 12345 before storing it in the database. When it’s retrieved with a SELECT
statement, the value is returned as an instance of a numeric data type (such as Number) rather than as a String instance.
The best way to avoid undesirable data type conversion is to follow two rules. First, define each column with the affinity
that matches the type of data that it is intended to store. Next, only insert values whose data type matches the defined
affinity. Following these rules provides two benefits. When you insert the data it isn’t converted unexpectedly (possibly
losing its intended meaning as a result). In addition, when you retrieve the data it is returned with its original data type.
For more information about the available column affinity types and using data types in SQL statements, see the “Data
type support” on page 1114.
Using synchronous and asynchronous database
operations
Adobe AIR 1.0 and later
Previous sections have described common database operations such as retrieving, inserting, updating, and deleting
data, as well as creating a database file and tables and other objects within a database. The examples have demonstrated
how to perform these operations both asynchronously and synchronously.
As a reminder, in asynchronous execution mode, you instruct the database engine to perform an operation. The
database engine then works in the background while the application keeps running. When the operation finishes the
database engine dispatches an event to alert you to that fact. The key benefit of asynchronous execution is that the
runtime performs the database operations in the background while the main application code continues executing.
This is especially valuable when the operation takes a notable amount of time to run.
On the other hand, in synchronous execution mode operations don’t run in the background. You tell the database
engine to perform an operation. The code pauses at that point while the database engine does its work. When the
operation completes, execution continues with the next line of your code.
A single database connection can’t execute some operations or statements synchronously and others asynchronously.
You specify whether a SQLConnection operates in synchronous or asynchronous when you open the connection to
the database. If you call SQLConnection.open() the connection operates in synchronous execution mode, and if you
call SQLConnection.openAsync() the connection operates in asynchronous execution mode. Once a
SQLConnection instance is connected to a database using open() or openAsync(), it is fixed to synchronous or
asynchronous execution.
Last updated 6/6/2012
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