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The Big Picture

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SQLMap is a simple but complete framework that makes it easy for you to map -your objects to your SQL statements or stored procedures. The goal of the -SQLMap framework is to obtain 80% of data access functionality using only -20% of the code.

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What does it do?

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Developers often create maps between objects within an application. One -definition of a Mapper is an "object that sets up communication between two -independent objects." A Data Mapper is a "layer of mappers that moves data -between objects and a database while keeping them independent of each other -and the mapper itself." [Patterns of Enterprise Architecture, ISBN -0-321-12742-0].

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You provide the database and the objects; SQLMap provides the mapping layer -that goes between the two.

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How does it work?

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Your programming platform already provides a capable library for accessing -databases, whether through SQL statements or stored procedures. But developers -find several things are still hard to do well when using "stock" PHP -function including:

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Separating SQL code from programming code Passing input parameters to the -library classes and extracting the output Separating data access classes from -business logic classes Caching often-used data until it changes Managing -transactions and many more -- by using XML documents to create a mapping -between a plain-old object and a SQL statement or a stored procedure. The -"plain-old object" can be any PHP object.

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Tip: -The object does not need to be part of a special object hierarchy or implement -a special interface. (Which is why we call them "plain-old" objects.) -Whatever you are already using should work just fine. -

- - alt="SQLMap DataMapper work flow" id="fig:diagram.png" class="figure"/> -
Figure 1: SQLMap DataMapper work flow
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Here's a high level description of the work flow shown in the figure above: -Provide a parameter, either as an object or a -primitive type. The parameter can be used to set runtime values in your SQL -statement or stored procedure. If a runtime value is not needed, the parameter -can be omitted.

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Execute the mapping by passing the parameter and the name you gave the -statement or procedure in your XML descriptor. This step is where the magic -happens. The framework will prepare the SQL statement or stored procedure, set -any runtime values using your parameter, execute the procedure or statement, -and return the result.

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In the case of an update, the number of rows affected is returned. In the case -of a query, a single object, or a collection of objects is returned. Like the -parameter, the result object, or collection of objects, can be a plain-old -object or a primitive type.

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So, what does all this look like in your source code? Here's how you might -code the insert of a "lineItem" object into your database.

- - -TMapper::instance()->insert("InsertLineItem", $lineItem); - - -

If your database is generating the primary keys, the generated key can be -returned from the same method call, like this:

- - -$myKey = TMapper::instance()->insert("InsertLineItem", $lineItem); - - -

The following example shows an XML descriptor for "InsertLineItem". - - - INSERT INTO [LinesItem] - (Order_Id, LineItem_LineNum, Item_Id, LineItem_Quantity, LineItem_UnitPrice) - VALUES - (#Order.Id#, #LineNumber#, #Item.Id#, #Quantity#, #Item.ListPrice#) - - select @@IDENTITY as value - - - -

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The <selectKey> stanza returns an auto-generated key from a SQL Server -database (for example). If you need to select multiple rows, SQLMap can return -a list of objects, each mapped to a row in the result set: - -$productList = Mapper::instance()->queryForList("selectProduct",$categoryKey); - -Or just one, if that's all you need: - -$product = Mapper::instance()->queryForObject("selectProduct",$categoryKey); - -

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Of course, there's more, but this is SQLMap from 10,000 meters. (For a longer, -gentler introduction, see the Tutorial.) -The Data Map definition files describes -where the statement for "InsertLineItem" would -be defined. The Installation and Setup section describes -the "bootstrap" configuration file that exposes SQLMap to your application.

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Is SQLMap the best choice for my project?

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SQLMap is a Data Mapping tool. Its role is to map the columns of a database -query (including a stored procedure) to the properties of an object. If your -application is based on business objects (including array or lists of -objects), then SQLMap can be a good choice. SQLMap is an even better choice -when your application is layered, so that that the business layer is distinct -from the user-interface layer.

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Under these circumstances, another good choice would be an Object/Relational -Mapping tool (OR/M tool), like [...]. Other products in this category are -[...] and [...] . An OR/M tool generates all or most of the SQL for you, -either beforehand or at runtime. These products are called OR/M tools because -they try to map an object graph to a relational schema.

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SQLMap is not an OR/M tool. SQLMap helps you map objects to stored procedures -or SQL statements. The underlying schema is irrelevant. An OR/M tool is great -if you can map your objects to tables. But they are not so great if your -objects are stored as a relational view rather than as a table. If you can -write a statement or procedure that exposes the columns for your object, -regardless of how they are stored, SQLMap can do the rest.

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So, how do you decide whether to OR/M or to DataMap? As always, the best -advice is to implement a representative part of your project using either -approach, and then decide. But, in general, OR/M is a good thing when you -

-Likewise, the best time to use a Data Mapper, like SQLMap, is when: - -

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In the end, you have to decide what's best for your project. If a OR/M tool -works better for you, that's great! If your next project has different needs, -then we hope you give SQLMap another look. If SQLMap works for you now: -Excellent!

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