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2009-06-09T07:27:37.997
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I've run into more problems than I hoped I would and as such I decided to dumb down the requirements for my first iteration. I'm currently trying to allow such Extensions only on the entire Company entity, in other words, I'm dropping the whole Owner requirement. So the problem could be rephrased as "How can I add virtual columns (entries in another entity that act like an additional column) to an entity at runtime?" My current implementation is as follow (irrelevant parts filtered out): <pre><code>@Entity class Company { // The set of Extension definitions, for example "Location" @Transient public Set<Extension> getExtensions { .. } // The actual entry, for example "Atlanta" @OneToMany(fetch = FetchType.EAGER) @JoinColumn(name = "companyId") public Set<ExtensionEntry> getExtensionEntries { .. } } @Entity class Extension { public String getLabel() { .. } public ValueType getValueType() { .. } // String, Boolean, Date, etc. } @Entity class ExtensionEntry { @ManyToOne(fetch = FetchType.EAGER) @JoinColumn(name = "extensionId") public Extension getExtension() { .. } @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "companyId", insertable = false, updatable = false) public Company getCompany() { .. } public String getValueAsString() { .. } } </code></pre> The implementation as is allows me to load a Company entity and Hibernate will ensure that all its ExtensionEntries are also loaded and that I can access the Extensions corresponding to those ExtensionEntries. In other words, if I wanted to, for example, display this additional information on a web page, I could access all of the required information as follow: <pre><code>Company company = findCompany(); for (ExtensionEntry extensionEntry : company.getExtensionEntries()) { String label = extensionEntry.getExtension().getLabel(); String value = extensionEntry.getValueAsString(); } </code></pre> There are a number of problems with this, however. Firstly, when using FetchType.EAGER with an @OneToMany, Hibernate uses an outer join and as such will return duplicate Companies (one for each ExtensionEntry). This can be solved by using Criteria.DISTINCT_ROOT_ENTITY, but that in turn will cause errors in my pagination and as such is an unacceptable answer. The alternative is to change the FetchType to LAZY, but that means that I will always "manually" have to load ExtensionEntries. As far as I understand, if, for example, I loaded a List of 100 Companies, I'd have to loop over and query each of those, generating a 100 SQL statements which isn't acceptable performance-wise. The other problem which I have is that ideally I'd like to load all the Extensions whenever a Company is loaded. With that I mean that I'd like that @Transient getter named getExtensions() to return all the Extensions for any Company. The problem here is that there is no foreign key relation between Company and Extension, as Extension isn't applicable to any single Company instance, but rather to all of them. Currently I can get past that with code like I present below, but this will not work when accessing referenced entities (if for example I have an entity Employee which has a reference to Company, the Company which I retrieve through employee.getCompany() won't have the Extensions loaded): <pre><code>List<Company> companies = findAllCompanies(); List<Extension> extensions = findAllExtensions(); for (Company company : companies) { // Extensions are the same for all Companies, but I need them client side company.setExtensions(extensions); } </code></pre> So that's were I'm at currently, and I have no idea how to proceed in order to get past these problems. I'm thinking that my entire design might be flawed, but I'm unsure of how else to try and approach it. Any and all ideas and suggestions are welcome!
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