Fstachecki at 09:48, 14 September 2018

2018-09-14T09:48:54Z

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[[Category:Drools Filip|095]]

== What is Domain Specific Language ==
[[File:ClipCapIt-160929-194441.PNG]]
* "A way of creating a rule language that is dedicated to your problem domain"
* DSL is a way non-technical people can write executable rules in Drools environment
* DSL is ultimately transformed to rules (mvel or java)
* .dsl file contain the transformations (mapping)
* DSLs have no impact on the rule engine at runtime, they are just a compile time feature

== When to use DSL ==
* Your requirements should be executable and always in sync with what is actually executed
* Analysts can focus on "logic proper"
* You already have rules written in SBVR or other standard (which is consistent and detailed enough to be easily translated into executable rules)
* You need "templates" for conditional elements and consequence actions that are used repeatedly in your rules (with minor variations)

== DSL in KIE Workbench==
Create New -> New DSL
[when]Order is greater than {totalOrder} = sc :ShoppingCart( $totalPrice : totalPrice > {totalOrder})
[then]Set discount to {discount} = sc.setTotalPrice( $totalPrice * (1-{discount}) ); update(sc);

# Create New -> New Rule
# Type (format) of rule: DSL or Guided Rule
dilect "mvel"
when
Order is greater than 10000
then
Set discount to 0.1

Use the test created for tall order discount

== Eclipse ==
See 08.1DSL folder

* '''DSLR''' file contains rules defined using business context
* '''DSL''' file contains the translations between business context and drools language

=== Connecting DSL file with DSRL file===
[[File:ClipCapIt-150716-052324.PNG]]

*'''It's not required to use expander to refer to DSL file in Drools 6.4 if all DSL files included in KIE Base are going to be used.'''
===DSL file===
* The DSL file is a text file containing DSL entries.
* Entry syntax
<source># This is a comment to be ignored</source>
[[File:ClipCapIt-160916-132246.PNG]]
* Examples
<source>
[condition][]There is a Shopping Cart that=$sc : ShoppingCart()
[consequence][]Show price=System.out.println($sc.totalPrice)
</source>
* <text expression> can contain Java regular expressions https://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html


====Nesting entries====
*Starting new entry with a hyphen sign "-" allows to add this expression to the last pattern
*Examples
<source>
[condition][]There is a Shopping Cart that=$sc : ShoppingCart()
[condition][]- total price is greater than 1000 =totalPrice > 1000
</source>
*Result
<source>
$sc : ShoppingCart(totalPrice > 1000)
</source>
* Hyphens can be used in consequence entries as part of a modify statement

====Variables====
*Variables can be defined using curly brackets { and }
*Examples
<source>
[condition][]There is a Shopping Cart that=$sc : ShoppingCart()
[condition][]- total price is greater than {price}=totalPrice >{price}
</source>
====Keywords====
* Keyword is valid in any part of DSLR file
<source>
[keyword] no loops = no-loop true
[keyword][]regula=rule
</source>

====String transformation functions====
<table border="1" cellpadding="10" cellspacing="0">
<tr bgcolor="#BDBDBD"><th>Name</th><th>Description</th></tr>
<tr><td>uc</td><td>Converts all letters to upper case.</td></tr>
<tr><td>lc</td><td>Converts all letters to lower case.</td></tr>
<tr><td>ucfirst</td><td>Converts the first letter to upper case, and all other letters to lower case.</td></tr>
<tr><td>num</td><td>Extracts all digits and "-" from the string. If the last two digits in the original string are preceded by "." or ",", a decimal period is inserted in the corresponding position.</td></tr>
<tr><td>a?b/c</td><td>Compares the string with string a, and if they are equal, replaces it with b, otherwise with c. But c can be another triplet a, b, c, so that the entire structure is, in fact, a translation table.</td></tr></table>
===== Examples=====
<source>
# definitions for conditions
[when][]There is an? {entity}=${entity!lc}: {entity!ucfirst}()
[when][]- with an? {attr} greater than {amount}={attr} >= {amount!num}
[when][]- with a {what} {attr}={attr} {what!positive?>0/negative?%lt;0/zero?==0/ERROR}
</source>

====Debug options for DSL expansion====
* Drools can log a DSL translation process
* To get access to those details use special type of statement starting with "#/ debug display"
<table border="1" cellpadding="10" cellspacing="0">
<tr bgcolor="#BDBDBD"><th>Word</th><th>Description</th></tr>
<tr><td>result</td><td>Prints the resulting DRL text, with line numbers.</td></tr>
<tr><td>steps</td><td>Prints each expansion step of condition and consequence lines.</td></tr>
<tr><td>keyword</td><td>Dumps the internal representation of all DSL entries with scope "keyword".</td></tr>
<tr><td>when</td><td>Dumps the internal representation of all DSL entries with scope "when" or "*".</td></tr>
<tr><td>then</td><td>Dumps the internal representation of all DSL entries with scope "then" or "*".</td></tr>
<tr><td>usage</td><td>Displays a usage statistic of all DSL entries.</td></tr></table>
===== Examples=====
<source>
#/ debug display result, steps and usage
#/ debug display result and usage
#/ debug display steps
</source>

Filip Drools - DSL - Revision history

Fstachecki at 09:48, 14 September 2018