Differences

This shows you the differences between two versions of the page.

--- at-m42:lecture14 [2009/04/26 10:10] – eechris
+++ at-m42:lecture14 [2011/01/14 12:45] (current) – external edit 127.0.0.1
@@ Line 462: / Line 462: @@
   * If you have a pool of connections you'd want to release your connection (returning it to the pool) when you've finished.
-====== Simplified Queries with Groovy =====
+=====  Simplified Queries with Groovy =====
 <code groovy 1|Example 2; Database lookup in Groovy (at-m42/Lectures/lecture14/Lookup.groovy)>
@@ Line 562: / Line 563: @@
 ===== Persistence Patterns: Transaction script =====
 In many applications it is natural to work directly with the relational model, issuing SQL queries and parsing result sets.
-  * This is known as the //[[http://martinfowler.com/eaaCatalog/transactionScript.html|Transaction Script]]// pattern((All patterns discussed in this lecture are from Fowler, //Patterns of Enterprise Application Architecture//.)): business logic is organized into procedures for each use case.
+  * This is known as the //[[http://martinfowler.com/eaaCatalog/transactionScript.html|Transaction Script]]// pattern((All patterns discussed in this lecture are from //Patterns of Enterprise Application Architecture//. See [[Recommended Reading]] for bibliographic details.)): business logic is organized into procedures for each use case.
   * Direct use of SQL is also well suited for aggregating queries and set-based updates (accessing large amounts of data or updating many tables in the same transaction)
 ===== Persistence Patterns: ORM =====
@@ Line 629: / Line 631: @@
-===== Some Issues that the Developers of an ORM Have to be Aware Of =====
-  * //Identity//: ensuring a record in a database is unique in a global sense.
-  * //Instantiated objects should be cached//: avoids a further trip to the database if it is needed in two separate transactions.
-  * "Dirty" objects (objects that have been created or changed in a transaction) //have to be committed to the database in a single atomic operation//.
-  * Objects that have not been changed do not need to be written back to the database.
-  * Queries may result in large numbers of records being returned from a database:
-    * Usually returned as a collection
-    * However objects in the collection should not be instantiated unless it is needed.
-===== Choosing a Persistence Strategy (1) =====
-  * Many enterprise applications need to use legacy databases, or share the database with other systems, so choices are limited!
-  * Despite the hype, it is rare for an enterprise to change its database supplier, so it is often not worth completely abstracting the details of a DBMS out of code.
-  * It is worth providing a data access layer so that your business logic does not talk directly JDBC but goes through a set of //Data Access Objects//.
-    * If the database schema changes, it will be in the access layer that changes will be needed, not in the business logic.
-    * If the business logic changes, again, persistence code changes are limited to the access layer.
-===== Choosing a Persistence Strategy (2) =====
-  * In some applications with a limited number of simple tables it will be quickest to use //active record// and talk directly to the database.
-  * If the application will require heavy use of set access, aggregation of data from many tables, or batch updates in many rows, a direct implementation using //transaction script// may be most efficient.
-  * ORM is a complex strategy which be of benefit only for complex domain models and or databases
-===== Choosing a Persistence Strategy (3) =====
-ORM can be of benefit if:
-  * Your application has the typical CRUD – create, retrieve, update, delete – workflow for domain objects.
-  * Objects are found in large sets but are updated and deleted individually.
-  * A large number of objects exist but they are "read-mostly"
-  * There is a natural mapping between classes and fields and database tables and records
-  * There are no unusual requirements such as the need to use customized SQL optimizations.
-  * For Java programmers ORM has the advantage of keeping SQL out of the code. But that is why we have DB architects!
 ===== Lecture Contents =====
-  * **[[#What is a Relational Database?|An introduction to relational databases and SQL]]**
+  * [[#What is a Relational Database?|An introduction to relational databases and SQL]]
   * [[#The Trouble with Databases|JDBC -- Java database connectivity API]]
-  * [[Immortal Objects]]
+  * [[#Immortal Objects]]
-  * [[Persistence Patterns]]
+  * [[#Persistence Patterns]]
-  * [[Other forms of Enterprise Integration]]
+  * **[[#Other forms of Enterprise Integration]]**
 ===== Other Forms of Enterprise Integration =====
   * Enterprise integration is not just about databases and SQL.
-  * Enterprise information systems such as:
+  * Enterprise information systms also often have to be built in to enterprise applications.
+  * Main technologies for this form of integration is the Java Connectivity API and Web Services.
+  * May not be talking Java so CORBA and similar technologies may come into play.
+----
+Some examples of enterprise information systems are:
   * Human Resources Systems
   * Payroll systems
@@ Line 676: / Line 656: @@
   * Business to Business Systems
   * Enterprise communication systems
-  * Other "legacy” systems
+  * Other //so-called// "legacy" systems
-  * 	also often have to be built in to enterprise applications.
-  * Main technologies are the Java Connectivity API and Web Services.
-  * May not be talking Java so CORBA and similar technologies come into play.
 ===== Lecture Summary =====
   * [[#What is a Relational Database?|An introduction to relational databases and SQL]]
   * [[#The Trouble with Databases|JDBC -- Java database connectivity API]]
-  * [[Immortal Objects]]
+  * [[#Immortal Objects]]
-  * [[Persistence Patterns]]
+  * [[#Persistence Patterns]]
-  * [[Other forms of Enterprise Integration]]
+  * [[#Other forms of Enterprise Integration]]
 ----
 [[Home]] | [[lecture13|Previous Lecture]] | [[Lectures]] | [[lecture15|Next Lecture]]