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https://issues.apache.org/jira/browse/TAPESTRY-1928?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12546957
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Howard M. Lewis Ship commented on TAPESTRY-1928:
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I think we're seeing a bigger issue here and it really related to the TextField
and Select components and not to the TypeCoercer service. The question is
how these components should handle blanks/nulls.
Workaround: don't use Booleans, create a ThreeState enum with values ON, OFF,
UNKNOWN.
> Coercion from null to Boolean yields false instead of null
> ----------------------------------------------------------
>
> Key: TAPESTRY-1928
> URL: https://issues.apache.org/jira/browse/TAPESTRY-1928
> Project: Tapestry
> Issue Type: Bug
> Components: tapestry-ioc
> Affects Versions: 5.0.6
> Reporter: Geoff Callender
>
> Boolean has 3 states: null, true, false, but the coercer coerces null to
> false. While this is correct behaviour for the boolean primitive (which has
> only 2 states), it is not correct for Boolean.
> The same argument applies here as in TAPESTRY-1648 which dealt with null
> BigDecimal and Integer.
> A practical consequence is that a BooleanValueEncoder that is 3-value aware
> becomes useless because the coercer will override it.
> For example I combined a BooleanValueEncoder with Select to allow a user to
> choose between "", "true", and "false". But when the user chooses "", they
> unexpectedly get the same result as choosing "false". Here's the template
> code:
> <select t:id="active" t:type="Select" value="active" model="actives"
> encoder="booleanValueEncoder"/>
> Here's the relevant java:
> static private final Boolean[] ACTIVES = { null, Boolean.TRUE,
> Boolean.FALSE };
> static private final BooleanValueEncoder BOOLEAN_VALUE_ENCODER = new
> BooleanValueEncoder();
> public Boolean getActive() {
> return _active;
> }
> public void setActive(Boolean active) {
> _active = active;
> }
> public Boolean[] getActives() {
> return ACTIVES;
> }
>
> public BooleanValueEncoder getBooleanValueEncoder() {
> return BOOLEAN_VALUE_ENCODER;
> }
> Here's a BooleanValueEncoder:
> public class BooleanValueEncoder implements ValueEncoder<Boolean> {
> public String toClient(Boolean value) {
> return value == null ? "" : value.toString();
> }
> public Boolean toValue(String clientValue) {
> return clientValue.equals("") ? null : Boolean.valueOf(clientValue);
> }
> }
> When the user chooses "", Tapestry calls setActive(Boolean.FALSE) instead of
> setActive(null).
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