Cross-Entity Variable Resolving and Arguments for ScriptTransformer Functions

Script Transformer has been widely used to modify the value of columns of selected rows from targeting data source (such as SQL Database) based on specific logics, before writing to Solr as documents. However, current implementation has the following limitations:
1. It is not possible to pass constant values or resolved variables (e.g., ${TABLE.COLUMN} ) as arguments to a script function.
2. Cross-entity row data exchange is not possible as well.

In our use case, we have complex nested entities and rely heavily on the script functions to transform table rows while doing data import. Sometimes for each single document, we need to get the selected column values from a parent entity into current entity for doing value transformation and applying if-else logics. To achieve this, we need to join with others tables in the SQL of current entity, which is quite resource-consuming, especially for large tables.

Therefore, we have done some improvements to allow us to pass selected column values from entity A to another entity B as its function arguments by utilizing variable resolver.

Here is an example about how it works. Suppose we have the following configuration:

<dataConfig>
    <dataSource name="ProductDB" 
                driver="oracle.jdbc.driver.OracleDriver" 
                url="jdbc:oracle:thin:@${dataimporter.request.host}:
                       ${dataimporter.request.port}/${dataimporter.request.name}" 
                user="${dataimporter.request.user}" 
                password="${dataimporter.request.password}" 
                autoCommit="true"/>
    <!-- ScriptTransformer functions -->
    <script><![CDATA[
        function processItemRow(row, resolvedVars) {
            var isOnSale = resolvedVars.get("${PRODUCT.IS_ONSALE}");
            var discount = resolvedVars.get("${PRODUCT.DISCOUNT_RATE}");
            var price = row.get("PRICE");
            
            if(isOnSale) {
              row.put("PRICE", price * discount);
            }
            else
              row.put("PRICE", price);
            
            return row;
        }
        ]]>
    </script>
    <document name="EC_SHOP">
        <entity dataSource="ProductDB" name="PRODUCT" 
                query="SELECT PRODUCT_ID, TITLE, IS_ONSALE, DISCOUNT_RATE FROM PRODUCT">
            <field column="PRODUCT_ID" name="PRODUCT_ID"/>
            <field column="TITLE" name="TITLE"/>
            <field column="IS_ONSALE" name="IS_ONSALE"/>
            <field column="DISCOUNT_RATE" name="DISCOUNT_RATE"/>               
            
            <entity dataSource="ProductDB" name="ITEM" 
                    transformer="script:processItemRow(${PRODUCT.IS_ONSALE},${PRODUCT.DISCOUNT_RATE})"
                    query="SELECT PRICE FROM ITEM WHERE PRODUCT_ID = '${PRODUCT.PRODUCT_ID}'">
                <field column="PRICE" name="PRICE"/>
            </entity>
        </entity>
    </document>
</dataConfig>

As demonstrated above, now we can get access to the value of column IS_ONSALE and DISCOUNT_RATE of table PRODUCT from the entity of table ITEM by passing ${PRODUCT.IS_ONSALE} and ${PRODUCT.DISCOUNT_RATE} as arguments of the function processItemRow to determine if we should give some discounts for the production price. The signature of function has a secondary argument (named resolvedVars here) for passing the map of column values resolved from other previous entities.

This improvement gives more flexibility for script functions to exchange row data cross entities (even cross datasource) and do more complex processing for entity rows.