Copy of Batch Metadata Expressions

Introduction

For the wishlist item MWISH-423 - Getting issue details... STATUS we want to introducte an expression language in order the describe the dynamical task requested by the customer.

Requirements

When executing a batch the new metadata of the item should be able to be determined by

• The previous/current metadata of the item

• Combinations of fields

• Conditions

• Textual operations

Solution

We create a new batch action “Metadata Expression” which takes as an argument a metadata sidecar e.g.

{
    "Descriptive": {
       "Title": "Metadata Expression Analysis"
    },
    "Dynamic": {
        "CustomField": "Some value"
    }
}

This metadata sidecar can now use a strict Spring Expression Language (Spel) subset to perform more complex operations. You can put one or more expressions #{...} in the JSON or XML. Inside an expression, you can reference the metadata using R(<Dotted key>) or record(<Dotted key>) for example R('Descriptive.Title') or record('Descriptive.Title').

Example input

{
    "Descriptive": {
       "Title": "R('Descriptive.Title').toUpperCase()",
       "Description": "R('Descriptive.Title') + ': ' + R('Dynamic.CustomField')",
       "Keywords": {"Keyword": "{R('Dynamic.CustomField')}"}
    },
    "Dynamic": {
        "CustomField": "R('Dynamic.CustomField2') == 'X' ? 'Option A' : 'Option B'"
    }
}

The output of the metadata accessor

The output of the metadata accessor R or record is the following depending on which field type the dotted key refers to:

The R takes an optional second argument, which is the default value. When it is not specified the default value is the empty string.

Security

The available features of SPel are described here: https://docs.spring.io/spring-framework/docs/3.2.x/spring-framework-reference/html/expressions.html. We must disable all features except

• Literal expressions

• Boolean and relational operators

• Method invocation

• Inline lists

• Ternary operator

• The method name “R” or “record”