When to Use It in Java

Generator QR Code in Java When to Use It
When to Use It
Generating QR Code 2d Barcode In Java
Using Barcode encoder for Java Control to generate, create Denso QR Bar Code image in Java applications.
Use Identity Field when there's a mapping between objects in memory and rows in a database This is usually when you use Domain Model (116) or Row Data Gateway (152) You don't need this mapping if you're using Transaction Script (110), Table Module (125), or Table Data Gateway (144)
Bar Code Encoder In Java
Using Barcode creation for Java Control to generate, create bar code image in Java applications.
For a small object with value semantics, such as a money or date range object that won't have its own table, it's better to use Embedded Value (268) For a complex graph of objects that doesn't need to be queried within the relational database, Serialized LOB (272) is usually easier to write and gives faster performance
Bar Code Scanner In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
One alternative to Identity Field is to extend Identity Map (195) to maintain the correspondence This can be used for systems where you don't want to store an Identity Field in the in-memory object Identity Map (195) needs to look up both ways: give me a key for an object or an object for a key I don't see this very often because usually it's easier to store the key in the object
QR Code Printer In C#
Using Barcode printer for .NET Control to generate, create QR Code image in VS .NET applications.
Further Reading
Generating QR Code In Visual Studio .NET
Using Barcode drawer for ASP.NET Control to generate, create QR Code ISO/IEC18004 image in ASP.NET applications.
[Marinescu] discusses several techniques for generating keys
Making Denso QR Bar Code In Visual Studio .NET
Using Barcode encoder for VS .NET Control to generate, create Quick Response Code image in .NET framework applications.
Example: Integral Key (C#)
Create Quick Response Code In VB.NET
Using Barcode generator for VS .NET Control to generate, create QR Code 2d barcode image in .NET applications.
The simplest form of Identity Field is a integral field in the database that maps to an integral field in an inmemory object
Printing Universal Product Code Version A In Java
Using Barcode generator for Java Control to generate, create UPC-A image in Java applications.
class DomainObject public const long PLACEHOLDER_ID = -1; public long Id = PLACEHOLDER_ID; public Boolean isNew() {return Id == PLACEHOLDER_ID;}
Barcode Encoder In Java
Using Barcode maker for Java Control to generate, create bar code image in Java applications.
An object that's been created in memory but not saved to the database will not have a value for its key For a NET value object this is a problem since NET values cannot be null Hence, the placeholder value
Drawing Bar Code In Java
Using Barcode creation for Java Control to generate, create barcode image in Java applications.
The key becomes important in two places: finding and inserting For finding you need to form a query using a key in a where clause In NET you can load many rows into a data set and then select a particular one with a find operation
EAN / UCC - 13 Creator In Java
Using Barcode printer for Java Control to generate, create UCC.EAN - 128 image in Java applications.
class CricketerMapper public Cricketer Find(long id) { return (Cricketer) AbstractFind(id); } class Mapper protected DomainObject AbstractFind(long id) { DataRow row = FindRow(id); return (row == null) null : Find(row); } protected DataRow FindRow(long id) { String filter = StringFormat("id = {0}", id);
Encode Code 128 Code Set C In Java
Using Barcode creation for Java Control to generate, create Code 128B image in Java applications.
DataRow[] results = tableSelect(filter); return (resultsLength == 0) null : results[0]; } public DomainObject Find (DataRow row) { DomainObject result = CreateDomainObject(); Load(result, row); return result; } abstract protected DomainObject CreateDomainObject();
Making ISSN - 13 In Java
Using Barcode generator for Java Control to generate, create ISSN - 10 image in Java applications.
Most of this behavior can live on the Layer Supertype (475), but you'll often need to define the find on the concrete class just to encapsulate the downcast Naturally, you can avoid this in a language that doesn't use compile-time typing
Code 3/9 Generator In VS .NET
Using Barcode maker for ASP.NET Control to generate, create Code 3/9 image in ASP.NET applications.
With a simple integral Identity Field the insertion behavior can also be held at the Layer Supertype (475)
Code 39 Full ASCII Maker In C#.NET
Using Barcode maker for Visual Studio .NET Control to generate, create ANSI/AIM Code 39 image in VS .NET applications.
class Mapper public virtual long Insert (DomainObject arg) { DataRow row = tableNewRow(); argId = GetNextID(); row["id"] = argId; Save (arg, row); tableRowsAdd(row); return argId; }
Creating EAN / UCC - 13 In Visual Studio .NET
Using Barcode printer for ASP.NET Control to generate, create EAN13 image in ASP.NET applications.
Essentially insertion involves creating the new row and using the next key for it Once you have it you can save the in-memory object's data to this new row
ANSI/AIM Code 39 Generation In Visual Basic .NET
Using Barcode generation for Visual Studio .NET Control to generate, create USS Code 39 image in .NET applications.
Example: Using a Key Table (Java)
Generating GTIN - 128 In VS .NET
Using Barcode maker for ASP.NET Control to generate, create GS1-128 image in ASP.NET applications.
by Matt Foemmel and Martin Fowler
Data Matrix ECC200 Drawer In .NET
Using Barcode drawer for VS .NET Control to generate, create Data Matrix 2d barcode image in Visual Studio .NET applications.
If your database supports a database counter and you're not worried about being dependent on databasespecific SQL, you should use the counter Even if you're worried about being dependent on a database you should still consider it as long as your key generation code is nicely encapsulated, you can always change it to a portable algorithm later You could even have a strategy [Gang of Four] to use counters when you have them and roll your own when you don't
Encode Code 128 In C#.NET
Using Barcode maker for .NET framework Control to generate, create Code 128 Code Set A image in .NET framework applications.
For the moment let's assume that we have to do this the hard way The first thing we need is a key table in the database
CREATE TABLE keys (name varchar primary key, nextID int) INSERT INTO keys VALUES ('orders', 1)
This table contains one row for each counter that's in the database In this case we've initialized the key to 1 If you're preloading data in the database, you'll need to set the counter to a suitable number If you want database-unique keys, you'll only need one row, if you want table-unique keys, you'll need one row per table
You can wrap all of your key generation code into its own class That way it's easier to use it more widely around one or more applications and it's easier to put key reservation into its own transaction
We construct a key generator with its own database connection, together with information on how many keys to take from the database at one time
class KeyGenerator private Connection conn; private String keyName; private long nextId; private long maxId; private int incrementBy; public KeyGenerator(Connection conn, String keyName, int incrementBy) { thisconn = conn; thiskeyName = keyName; thisincrementBy = incrementBy; nextId = maxId = 0; try { connsetAutoCommit(false); } catch(SQLException exc) { throw new ApplicationException("Unable to turn off autocommit", exc); } }
We need to ensure that no auto-commit is going on since we absolutely must have the select and update operating in one transaction
When we ask for a new key, the generator looks to see if it has one cached rather than go to the database
class KeyGenerator public synchronized Long nextKey() { if (nextId == maxId) { reserveIds(); } return new Long(nextId++); }