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Chapter 11
Data Type Conversion

This chapter describes how the JavaScript runtime engine on the server converts between the more complex data types used in relational databases and the simpler ones defined for JavaScript.

This chapter contains the following sections:


About Data Type Conversion

Databases have a rich set of data types. The JavaScript runtime engine on the server converts these data types to JavaScript values, primarily either strings or numbers. A JavaScript number is stored as a double-precision floating-point value. In general, the runtime engine converts character data types to strings, numeric data types to numbers, and dates to JavaScript Date objects. It converts null values to JavaScript null.

NOTE: Because JavaScript does not support fixed or packed decimal notation, some precision may be lost when reading and writing packed decimal data types. Be sure to check results before inserting values back into a database, and use appropriate mathematical functions to correct for any loss of precision.

Working with Dates and Databases

Date values retrieved from databases are converted to JavaScript Date objects. To insert a date value in a database, use a JavaScript Date object, as follows:

cursorName.dateColumn = dateObj
Here, cursorName is a cursor, dateColumn is a column corresponding to a date, and dateObj is a JavaScript Date object. You create a Date object using the new operator and the Date constructor, as follows:

dateObj = new Date(dateString)
where dateString is a string representing a date. If dateString is the empty string, it creates a Date object for the current date. For example:

custs.orderDate = new Date("Jan 27, 1997")
NOTE: DB2 databases have time and timestamp data types. These data types both convert to the Date type in JavaScript.
WARNING: The LiveWire Database Service cannot handle dates after February 5, 2037.
For more information on working with dates in JavaScript, see "Date Object."


Data-Type Conversion by Database

The following table shows the conversions made by the JavaScript runtime engine for DB2 databases.

Table 11.1 DB2 data-type conversions  

DB2 Data Type JavaScript Data Type

char(n), varchar(n), long varchar, clob(n)

string

integer, smallint

integer

decimal, double

double

date, time, timestamp

Date

blob

Blob

The following table shows the conversions made by the JavaScript runtime engine for Informix databases.

Table 11.2 Informix data-type conversions  

Informix Data Type JavaScript Data Type

char, nchar, text, varchar, nvarchar

string

decimal(p,s), double precision, float, integer, money(p,s), serial, smallfloat, smallint

number

date, datetime1

Date

byte

Blob

interval

Not supported

1 The Informix datetime data type has variable precision defined by the user. Server-side JavaScript displays datetime data with the format of YEAR to SECOND. If a datetime variable has been defined with another precision, such as MONTH to DAY, it may display incorrectly. In this situation, the data is not corrupted by the incorrect display.

ODBC translates a vendor's data types to ODBC data types. For example, the Microsoft SQL Server varchar data type is converted to the ODBC SQL_VARCHAR data type. For more information, see the ODBC SDK documentation. The following table shows the conversions made by the JavaScript runtime engine for ODBC databases.

Table 11.3 ODBC data-type conversions  

ODBC Data Type JavaScript Data Type

SQL_LONGVARCHAR, SQL_VARCHAR, SQL_CHAR

string

SQL_SMALLINT, SQL_INTEGER, SQL_DOUBLE, SQL_FLOAT, SQL_REAL, SQL_BIGINT, SQL_NUMERIC, SQL_DECIMAL

number

SQL_DATE, SQL_TIME, SQL_TIMESTAMP

Date

SQL_BINARY, SQL_VARBINARY, SQL_LONGBINARY

Blob

The following table shows the conversions made by the JavaScript runtime engine for Oracle databases.

Table 11.4 Oracle data-type conversions  

Oracle Data Type JavaScript Data Type

long, char(n), varchar2(n), rowid

string

number(p,s), number(p,0), float(p)

number

date

Date

raw(n), long raw

Blob

The following table shows the conversions made by the JavaScript runtime engine for Sybase databases.

Table 11.5 Sybase data-type conversions  

Sybase Data Type JavaScript Data Type

char(n), varchar(n), nchar(n), nvarchar(n), text

string

bit, tinyint, smallint, int, float(p), double precision, real, decimal(p,s), numeric(p,s), money, smallmoney

number1

datetime, smalldatetime

Date

binary(n), varbinary(n), image

Blob

1 The Sybase client restricts numeric data types to 33 digits. If you insert a JavaScript number with more digits into a Sybase database, you'll get an error.


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Last Updated: 09/29/99 18:01:59

© Copyright 1999 Sun Microsystems, Inc. Some preexisting portions Copyright 1999 Netscape Communications Corp. All rights reserved.