Hi all, as discussed during the last meeting I'm looking into adding support for enum columns in GeoPackage. Enumerations are made possible by the schema options, and in particular, by the gpkg_data_columns table along with the gpkg_data_column_constraints one.
The latter can contain an association between integer value and their description, allowing to build an enumeration. During the meeting Jody mentioned CodeList as a possible way to represent an enumeration, so I looked into it. A CodeList is an abstract class representing an extensible enumeration: https://github.com/geotools/geotools/blob/25015cd04354e315913961bbc5b9bd3db87c6242/modules/library/opengis/src/main/java/org/opengis/util/CodeList.java#L34 The class has many subclasses, one for each type of extensible enumeration the code wants to handle .e.g.: [image: image.png] This implies the name and initial contents of the enumeration must be known at compile time, while in GeoPackage we'll discover them at runtime. It does not seem the way to go, a new enumeration could have to be created for each column and table in a GeoPackage (this is an extreme, but in my use case I have tables with 6-7 different enumerated columns, and various tables using enumerations in general). The enumeration definition must not keep permanent space, or it would turn into a memory leak in a long running application processing many different GeoPackages. Also, their values are best handled by all other formats and stores without too many modifications. Looking around it seems the simplest solution is to go with String representations, along with a pool of values that would make most of those String objects just pointers to common objects (the store would take care of that), and leverate the AttributeDescriptor restriction. This approach is already currently used for the column length restrictions: https://github.com/geotools/geotools/blob/93442c6b374b1d14169f43841955bb2b695127c5/modules/library/main/src/main/java/org/geotools/feature/AttributeTypeBuilder.java#L392 in particular, a Filter looking like "LengthFunction(attribute) <= maxLenght" is built to represent the situation, and a utility method in FeatureTypes is used to extract the max lenght of a field, here: https://github.com/geotools/geotools/blob/029dc5c8ccc503de3cfd7f4d1c939d8056c260c4/modules/library/main/src/main/java/org/geotools/feature/FeatureTypes.java#L135 I plan to do the same, have an OR filter with equalities with the possible values to represent the enum possible values, and a method in FeatureTypes to easily extract said list. Maybe extend the attribute and feature type builders with an easy way to build an enumerated attribute too. How does that sound? Cheers Andrea == GeoServer Professional Services from the experts! Visit http://goo.gl/it488V for more information. == Ing. Andrea Aime @geowolf Technical Lead GeoSolutions S.A.S. Via di Montramito 3/A 55054 Massarosa (LU) phone: +39 0584 962313 fax: +39 0584 1660272 mob: +39 339 8844549 http://www.geo-solutions.it http://twitter.com/geosolutions_it ------------------------------------------------------- *Con riferimento alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni circostanza inerente alla presente email (il suo contenuto, gli eventuali allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le sarei comunque grato se potesse darmene notizia. This email is intended only for the person or entity to which it is addressed and may contain information that is privileged, confidential or otherwise protected from disclosure. We remind that - as provided by European Regulation 2016/679 “GDPR” - copying, dissemination or use of this e-mail or the information herein by anyone other than the intended recipient is prohibited. If you have received this email by mistake, please notify us immediately by telephone or e-mail.*
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