Re: Derived attribute

Thank you Andrus,

How would I do a query to fetch all where absDelta > 10 for example?



> On Sep 26, 2025, at 12:16=E2=80=AFPM, Andrus Adamchik =
<[email protected]> wrote:
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> Hi Ricardo,
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> "defaultValueExpression" is a hallucination. There's nothing like that =
in Cayenne :) Taking it out of the model and into Java will work:
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> 1. A getter (like you mentioned) :
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>   public BigDecimal getAbsDelta() {
>      return getDelta().abs();
>   }
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> 2. An expression for WHERE:
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>   Expression e =3D FunctionExpressionFactory.absExp("delta");
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> 3. An ordering:
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>   Ordering o =3D new Ordering(e);
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> Thanks,
> Andrus
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>> On Sep 26, 2025, at 10:48=E2=80=AFAM, Ricardo Parada =
<[email protected]> wrote:
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>> Hello,
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>> I=E2=80=99m looking into what we should do with derived attributes we =
have defined in our EOF object models after migrating to Cayenne.=20
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>> I would like to be able to use the derived attribute in queries in =
the where clause and order by clause.=20
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>> For example, if my entity has a DELTA column and a derived column =
ABS_DELTA that uses ABS(DELTA) expression when fetching it or when used =
in the where clause or order by clause.=20
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>> ChatGPT suggested using defaultValueExpression as one of the options =
but cautioned it would not work with 5.0-M1. Something like this:
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>> <db-entity name=3D"MY_ENTITY" schema=3D"public">
>>   <db-attribute name=3D"ID" type=3D"INTEGER" isPrimaryKey=3D"true" =
isMandatory=3D"true"/>
>>   <db-attribute name=3D"DELTA" type=3D"DECIMAL"/>
>>   <db-attribute name=3D"ABS_DELTA" type=3D"DECIMAL" =
isGenerated=3D"true">
>>       <defaultValueExpression>ABS(DELTA)</defaultValueExpression>
>>   </db-attribute>
>> </db-entity>
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>> <obj-entity name=3D"MyEntity" className=3D"com.example.model.MyEntity" =
dbEntityName=3D"MY_ENTITY">
>>   <obj-attribute name=3D"id" type=3D"java.lang.Integer" =
db-attribute-path=3D"ID"/>
>>   <obj-attribute name=3D"delta" type=3D"java.math.BigDecimal" =
db-attribute-path=3D"DELTA"/>
>>   <obj-attribute name=3D"absDelta" type=3D"java.math.BigDecimal" =
db-attribute-path=3D"ABS_DELTA"/>
>> </obj-entity>
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>> It also mentioned using something like this:
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>> Property.create("absDelta", BigDecimal.class).alias("ABS(DELTA)").
>> Does anybody have any suggestions or recommendations? I would prefer =
something that works with 5.0-M1 since by the time we do this migration =
I=E2=80=99m thinking we would use the latest version which will be 5.0 =
by that time. =20
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>> I think that something that allows me to use the derived columns in =
the where and order by clause. In most cases it would be okay to =
additionally write the logic in Java so that in-memory sorting / =
filtering works. For example, a getAbsDelta() that returns =
Math.abs(getDelta()).=20
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>> Thank you
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>> Ricardo Parada
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