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POHow to dynamically add a property / field to a domain class in Grails?
 

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  1. POHow to dynamically add a property / field to a domain class in Grails?
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    <p>For a project I'm currently working on I need to dynamically add properties to a domain class and persist them later in the database. In general, I need a key/value store attached to a "normal" domain class. Sadly I cannot use a NoSQL database (e.g. Redis). </p> <p>My approach would be to handle the additional properties on a <code>save()</code> by identifying them within <code>afterInsert</code> or <code>afterUpdate</code> and writing them to another table - I would prefer not to use a map property within the domain class but an additional "Field" table (to better support searches).</p> <p>I tried to add properties using the <strong>metaClass approach</strong>:</p> <pre><code>person.metaClass.middlename = "Biterius" assert person.middlename == "Biterius" // OK </code></pre> <p>This works and I can identify the additional properties in the afterInsert/afterUpdate methods but it seems that I cannot change the value thereafter - i.e., the following does not work:</p> <pre><code>person.middlename = "Tiberius" assert person.middlename == "Tiberius" // FAIL </code></pre> <p>Then I tried an <strong>Expando approach</strong> by extending the Person class by the Expando class (directly ("Person extends Expando") and via an abstract intermediate class ("Person extends AbstractPerson" and "AbstractPerson extends Expando")). </p> <pre><code>def person = new Person() assert person in Person // OK assert person in AbstractPerson // OK assert person in Expando // OK </code></pre> <p>Both variants did not work - I could assign values to arbitrary "properties" but the values were not stored!</p> <pre><code>person.mynewproperty = "Tiberius" // no MissingPropertyException is thrown println person.mynewproperty // returns null </code></pre> <p>So how can I add properties to a domain class programmatically during runtime, change them and retrieve them during afterInsert or afterUpdate in order to "manually" store them in a "Fields" table? </p> <p>Or am I doing something completely wrong? Are there other / simpler ways to do this?</p>
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    1. USJörg Rech
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    1. COAre you trying to save metadata or are you actually trying to add a column to a table dynamically? A bit confused
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      1. USchrislovecnm
    2. COSo the field table would generate one table for each new property? Is that what you are looking for?
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      1. POHow to dynamically add a property / field to a domain class in Grails?
      1. USJeff Beck
    3. CO@chrislovecnm I'm trying to add a column to tables dynamically. For example, adding a "Middlename" to a Person table.
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      1. USJörg Rech
 

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