An update: SetPrice

A <Lambda> can also be used to update a database.

Definition

A <Lambda> for an update operation is declared in the same way as one for a search operation.

For example, in your schemas folder, open SetPrice.xml. This schema is very similar to the <GetCoffee> schema created in the previous tutorial section. Open SetPrice-declaration.xml. Note that the return type is set to <http://waterken.com/Void>, since an SQL update statement does not produce a result set. Two parameters are necessary for this update: the coffee name and price.

A <http://waterken.com/coffeebreak/SetPrice> resource embodies the authority to update the price of any coffee.

Structure

The only difference between an update <Lambda> and the previously seen <GetCoffee> <Lambda> is that an update <Lambda> wraps an SQL update resource, instead of an SQL query resource.

For example, open the <SetPrice> resource at <revywcgymlra7na6hn5nk5i6bu.xml>.

The <Lambda>'s type is <SetPrice>. The statement link refers to an <http://waterken.com/sql/update/Statement>. The price parameter is protected by an <UnsignedDouble> guard, and name is unrestricted.

Run it

Click here to view the representation on your machine. Try setting a price.

This resource is hard to use because the client must enter the coffee name and price. The coffee name has to correspond exactly to the name in the database. The client cannot see the price before changing it nor after. We can easily ameliorate this situation by binding the coffee name argument to the resource. Later in the tutorial we will combine editing and viewing of a coffee price.

The next section describes binding arguments.

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