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According to [PoEAA], this definition is "A Domain Model creates a web of interconnected objects, where each object represents some meaningful individual, whether as large as a corporation or as small as a single line on an order form." Domain Model has two kinds of type: Simple Domain Model: Every domain model can be mapped to one database table. Usually it uses Active Record. Complex Domain Model: The model uses inheritance, strategies and other design patterns. Database can not directly map to the model. Using Data Mapper is required. 1.1 When to use it If the business layer is frequently...

According to [PoEAA], this definition is "A Transaction Script organizes all this logic primarily as a single procedure, making calls directly to the database or through a thin database wrapper." For example, when I buy a book on a ecommerce shop, the system executes a series of action, including receiving a book id and customer session, getting a book detail and customer detail from the database, and inserting an order into the database. These actions are organized in a transaction script. Usually, a database transaction maps to a transaction script. So it is easily to implement data isolat...

Avoiding NullPointerException In this article, we'll explore the main techniques to fight it: the self-validating model and the Optional wrapper. by The terrible NullPointerException (NPE in short) is the most frequent Java exception occurring in production, according to a 2016 study. In this article, we'll explore the main techniques to fight it: the self-validating model and the Optional wrapper. Self-Validating Model Imagine a business rule: every Customer has to have a birth date set. There are a number of ways to implement this constraint: validating the user data on the create and up...