`<switch>`

<switch> creates a set of conditional statements in which each condition triggers a specific response from the system.

Description

Note: <switch> may be used only within a <block>.

The <switch> construct is an extended for of the <if>/<then> construct that makes it easier to contain conditional logic in the same construct (e.g., using a single <switch> instead of many <if>/<then>) statements.

<switch> has two different versions of its syntax that can be used. The first is bound to a scalar variable using the on attribute in the opening <switch> tag. The second form allows for comparisons to an arbitrary number of scalar variables, or other expressions that resolve to 0 or 1 (otherwise known as a boolean expression).

Syntax

<switch on="[VAR]"> 
  <case when="{[CONDITION_1]}">  
    [CONTENTS_1]
  </case> 
  <case when="{[CONDITION_2]}">  
    [CONTENTS_2] 
  </case> 
... 
  <else>  
    [CONTENTS_0]
  </else>
</switch>

This expands to [CONTENTS_1] if [VAR] is [CONDITION_1], [CONTENTS_2] if [VAR] is [CONDITION_2], and so on, or [CONTENTS_0] if [VAR] does not match any of the cases.

Note: The <else> clause may be omitted, in which case nothing is inserted if there is no match.

Alternate syntax

<switch> 
  <case when="{[VAR_1][COMPARISON][CONDITION_1]}">  
    [CONTENTS_1] 
  </case> 
  <case when="{[VAR_2][COMPARISON][CONDITION_2]}">  
    [CONTENTS_2] 
  </case> 
  <case when="{[BOOLEAN_EXPRESSION]}">  
    [CONTENTS_3] 
  </case> 
...
  <else>  
    [CONTENTS_0]
  </else>
</switch>

Each of the [CONDITION_1], [CONDITION_2], ... must be 0 or 1. In this version, the first case with when="1" is inserted. If no condition is matched, [CONTENTS_0] is inserted.

Note: The <else> clause may be omitted, in which case nothing is inserted if there is no match.

Attributes

on: on specifies the value or variable that each <case> permutation will compare to its specific conditions. Can be any value or may be omitted.

Example: `<switch>` Form 1

In this example, the base table is pub.demo.retail.item, and the objective is to select any one store in the table or all stores.

<base table="pub.demo.retail.item"/>
<defblock name="storeselect" type="store" store="2">
    <switch on="{@type}">
        <case when="all">
            <note>all stores selected</note>
        </case>
        <case when="store">
            <sel value="store={@store}"/>
        </case>
      <else>
            <signal msg="Please make a selection"/>
       </else>
    </switch>
</defblock>
<insert block="storeselect" type="store" store="1"/>

`<switch>` Form 2

The second form of the <switch> statement is ideal for use in cases when the behavior of the query is dependent on more than a single variable, such as basic error checking. In this form, the on attribute is omitted, as follows:

<base table="pub.demo.retail.item"/>
<defblock name="testswitchformtwo" store_select="" sku_select="" 
 account_select="">
    <switch>
        <case when="{@store_select=''}">
            <signal msg="You must select a store value"/>
        </case>
        <case when="{@sku_select=''}">
            <signal msg="You must select a product"/>
        </case>
        <case when="{@account_select=''}">
            <signal msg="You must select an account"/>
        </case>
        <else>
            <sel value="store={@store_select} & sku={@sku_select} 
                        & account={@account_select}"/>
        </else>
    </switch>
</defblock>
<insert block="testswitchformtwo" store_select="1" sku_select="366" 
 account_select="957"/>

<switch>