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**Isomorphic** · 17 Jan 2011, 11:54

optionDataSource is not the right way to do this (in fact it's not valid to set it in the DataSource - it's on ListGridField and FormItem only).

JXPath is the typical approach, but since you're having trouble with that, you can replicate the functionality by adding a DMI that takes the result of dsResponse.getRecords() and adds the additional property you need by ordinary Java code.

If it's a recurring pattern, create a custom DataSource that does this via a custom property you add to the DataSourceField - essentially your own, simplified version of the JXPath feature that isn't working for you with GAE.

**atomatom** · 17 Jan 2011, 12:10

Thanks for the quick reply.

I had been seriously considering the approach you suggest with extra properties. The thing I'm not sure about is;

1) Do I just add new fields to a record to represent the property (seems ugly, and difficult to handle)

2) Do I create a new type 'type="pair_DataSource"' which I can use to pass back a displayValue/fieldValue pair, and then add custom CellFormatter to display it.

I got a bit lost on the correct way to encode 2). On the server side, I presume I can go something like DataTools.setProperties(pair,map);

This is all sounds far too convoluted. I think I should try and get XPath working...

**Isomorphic** · 17 Jan 2011, 12:13

This is what it looks like for SQL. You declare an additional field for the display value which is found in a related table, and you use a join to retrieve it.

Very simple to the equivalent thing in Java, just replace the join with ordinary Java code to get the display value from the related bean.

Definitely would not recommend your #2 approach, which does sound complicated.

**atomatom** · 17 Jan 2011, 14:42

Hmm, interesting. I presume all the table tags are only used by the SQL datasource and don't mean anything to the client components?

I think I understand the SQL example. I'm a little unclear of the parts that are missing to do it as a Java DMI. I presume pretty much that I just return the same results that the join would. But do I need to do any other special handling to deal with the 'tableName' or other tags?

**Isomorphic** · 17 Jan 2011, 14:45

Ignore all the SQL artifacts (and note, the client doesn't even receive this information). The key take-away is that you just add another field to carry the display value, and add Java code to place it into the returned data.

**atomatom** · 18 Jan 2011, 04:29

Thanks so much. The simple approach of adding new fields makes this so much easier. I was getting seriously stuck abusing existing functionality to do something it was not meant to do.

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optionDataSource (and alternatives) and JPA/GAE

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