Update in ibatis

It is not meant as a object-to-relational mapping tool. There are many frameworks that provide extensive object-to-relational mapping features. The six statement-type elements take various attributes. The individual attributes are described in the sections that follow.

A Parameter Map defines an ordered list of values that match up with the "? The first "? The second is replaced with the description property. However, Parameter Maps are useful when the SQL must be kept in a standard form or when extra information needs to be provided. For more about Parameter Maps see Section 3. If a parameterMap attribute is not specified, you may specify a parameterClass instead and use inline parameters see Section 3.

The value of the parameterClass attribute can be a Type Alias or the fully qualified name of a class. A Result Map lets you control how data is extracted from the result of a query, and how the columns are mapped to object properties. If you want all the columns, you don't need to map them all individually. Though many developers consider it a good practice to always specify the columns expected. If a resultMap is not specified, you may specify a resultClass instead.

The value of the resultClass attribute can be a Type Alias or the fully qualified name of a class. The class specified will be automatically mapped to the columns in the result, based on the result metadata. Each of these corresponds with the column aliases described by the SQL select statement using the " as " keyword —a standard SQL feature. When executed, a Person object is instantiated and populated by matching the object property names to the aliased column names from the query.

There is no way to specify the types of the output columns if needed , there is no way to automatically load related data such as complex properties, and there is a slight performance consequence from accessing the result metadata.

Architecturally, using aliases this way mixes database logic with reporting logic , making the query harder to read and maintain. You can overcome these limitations with an explicit Result Map Section 3.

In addition to providing the ability to return an IList of objects, the DataMapper supports the use of a strongly-typed custom collection: a class that implements the System. CollectionBase abstract class. The following is an example of a CollectionBase class that can be used with the DataMapper.

A CollectionBase class can be specified for a select statement through the listClass attribute. The value of the listClass attribute can be a Type Alias or the fully qualified name of a class. The statement should also indicate the resultClass so that the DataMapper knows how to handle the type of objects in the collection. The resultClass specified will be automatically mapped to the columns in the result, based on the result metadata. For more about Cache Models, see Section 3.

When writing Sql, you often encounter duplicate fragments of SQL. For all these reasons, file systems are not considered a good data-storage solution when persistence is desired.

The most common approach today is to use databases that serve as repositories for large amounts of data. There are many types of databases: relational, hierarchical, network, object-oriented, and so on.

These databases, along with their database management systems DBMSs , not only provide a persistence facility, but also manage the information that is persisted. Relational databases are the mostly widely used type. Data in a relational database is modeled as a set of interrelated tables. The advent of enterprise applications popularized the n-tier architecture , which aims to improve maintainability by separating presentation, business, and database-related code into different tiers or layers of the application.

The layer that separates the business logic and the database code is the persistence layer , which keeps the application independent of the underlying database technology. With this robust layer in place, the developer no longer needs to take care of data persistence. The persistence layer encapsulates the way in which the data is stored and retrieved from a relational database. JDBC code is embedded in Java classes -- in other words, it's tightly coupled to the business logic.

This code also relies heavily on SQL, which is not standardized across databases; that makes migrating from one database to another difficult. Relational database technology emphasizes data and its relationships, whereas the object-oriented paradigm used in Java concentrates not on the data itself, but on the operations performed on that data.

Here a condition would be added only when a passed property is not empty. If you pass an ID, then it returns records corresponding to that ID Otherwise, it returns all the records. Try the above example by passing null as smc.

The most common thing to do in dynamic SQL is conditionally include a part of a where clause. This statement provides an optional text search type of functionality. If you pass in no title, then all active Blogs are returned.

But if you do pass in a title, it will look for a title with the given like condition. It helps choose only one case among many options. The following example would search only by title if one is provided, then only by author if one is provided. Take a look at our previous examples to see what happens if none of the conditions are met. The foreach element allows you to specify a collection and declare item and index variables that can be used inside the body of the element.

It also allows you to specify opening and closing strings, and add a separator to place in between iterations. Assuming you are going to use Log4J for logging. Following is the log4j. Note that some of the lines are commented out. You can uncomment them if you need additional debugging information. The following Java class is a very simple example that initializes and then uses the Log4J logging library for Java applications.