Package org.apache.sis.feature

# Class FeatureOperations

Object
Static
FeatureOperations

public final class FeatureOperations extends Static
A set of pre-defined operations expecting a `Feature` as input and producing an `Attribute` as output. Those operations can be used for creating dynamic properties which compute their value on-the-fly from the values of other properties.

A flexible but relatively cumbersome way to define arbitrary computations is to subclass `AbstractOperation`. This `FeatureOperations` class provides a more convenient way to get a few commonly-used operations.

## Operation name, designation and description

All operations are identified by a programmatic name, but can also have a more human-readable designation for Graphical User Interfaces (GUI). Those identification information are specified in a `Map<String,?>`. The recognized entries are the same than the ones documented in `AbstractIdentifiedType`, augmented with entries that describe the operation result. Those entries are summarized below:

Recognized map entries
Map key | Value type | Returned by
--- | --- | ---
"name" | `GenericName` or `String` | `Operation.getName()` (mandatory)
"definition" | `InternationalString` or `String` | `Operation.getDefinition()`
"designation" | `InternationalString` or `String` | `Operation.getDesignation()`
"description" | `InternationalString` or `String` | `Operation.getDescription()`
"result.name" | `GenericName` or `String` | `Attribute.getName()` on the result
"result.definition" | `InternationalString` or `String` | `Attribute.getDefinition()` on the result
"result.designation" | `InternationalString` or `String` | `Attribute.getDesignation()` on the result
"result.description" | `InternationalString` or `String` | `Attribute.getDescription()` on the result
"locale" | `Locale` | (none)

If no `"result.*"` entry is provided, then the methods in this class will use some default name, designation and other information for the result type. Those defaults are operation specific; they are often, but not necessarily, the same than the operation name, designation, etc.

Since:
  0.7

Defined in the `sis-feature` module

- ## Method Summary

  Modifier and Type
  Method
  Description
  `static AbstractOperation`
  `compound(Map<String,?> identification, String delimiter, String prefix, String suffix, AbstractIdentifiedType... singleAttributes)`
  Creates an operation concatenating the string representations of the values of multiple properties.
  `static AbstractOperation`
  `envelope(Map<String,?> identification, CoordinateReferenceSystem crs, AbstractIdentifiedType... geometryAttributes)`
  Creates an operation computing the envelope that encompass all geometries found in the given attributes.
  `static AbstractOperation`
  `link(Map<String,?> identification, AbstractIdentifiedType referent)`
  Creates an operation which is only an alias for another property.

  ### Methods inherited from class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Method Details

  - ### link

    public static AbstractOperation link(Map<String,?> identification, AbstractIdentifiedType referent)
    Creates an operation which is only an alias for another property.
    Example: features often have a property that can be used as identifier or primary key. But the name of that property may vary between features of different types. For example features of type Country may have identifiers named “ISO country code” while features of type Car may have identifiers named “license plate number”. In order to simplify identifier usages regardless of their name, an application could choose to add in all features a virtual property named `"identifier"` which links to whatever property is used as an identifier in an arbitrary feature. So the definition of the Car feature could contain the following code:

    >     AttributeType licensePlateNumber = ...;            // Attribute creation omitted for brevity
    >     FeatureType car = new DefaultFeatureType(...,      // Arguments omitted for brevity
    >             licensePlateNumber, model, owner,
    >             FeatureOperations.link(singletonMap(NAME_KEY, "identifier"), licensePlateNumber);

    Since this method does not create new property (it only redirects to an existing property), this method ignores all `"result.*"` entries in the given `identification` map.

    #### Read/write behavior

    Since the `Operation​.apply(…)` method returns directly the property identified by the `referent` argument, the returned property is writable if the referenced property is also writable.
    Warning: The type of `referent` parameter will be changed to `PropertyType` if and when such interface will be defined in GeoAPI.
    Parameters:
      `identification` - the name and other information to be given to the operation.
      `referent` - the referenced attribute or feature association.
    Returns:
      an operation which is an alias for the `referent` property.
    See Also:
      - `Features​.getLinkTarget(PropertyType)`

  - ### compound

    public static AbstractOperation compound(Map<String,?> identification, String delimiter, String prefix, String suffix, AbstractIdentifiedType... singleAttributes) throws UnconvertibleObjectException
    Creates an operation concatenating the string representations of the values of multiple properties. This operation can be used for creating a compound key as a `String` that consists of two or more attribute values that uniquely identify a feature instance.

    The `delimiter`, `prefix` and `suffix` arguments given to this method are used in the same way than `StringJoiner`, except for null values. Null prefix, suffix and property values are handled as if they were empty strings.

    If the same character sequences than the given delimiter appears in a property value, the `'\'` escape character will be inserted before that sequence. If the `'\'` character appears in a property value, it will be doubled.

    #### Restrictions

    - The single properties can be either attributes or operations that produce attributes; feature associations are not allowed, unless they have an `"sis:identifier"` property.
    - Each attribute shall contain at most one value; multi-valued attributes are not allowed.
    - The delimiter can not contain the `'\'` escape character.

    #### Read/write behavior

    This operation supports both reading and writing. When setting a value on the attribute created by this operation, the given string value will be split around the `delimiter` and each substring will be forwarded to the corresponding single property.
    Warning: The type of `singleAttributes` elements will be changed to `PropertyType` if and when such interface will be defined in GeoAPI.
    Parameters:
      `identification` - the name and other information to be given to the operation.
      `delimiter` - the characters to use as delimiter between each single property value.
      `prefix` - characters to use at the beginning of the concatenated string, or `null` if none.
      `suffix` - characters to use at the end of the concatenated string, or `null` if none.
      `singleAttributes` - identification of the single attributes (or operations producing attributes) to concatenate.
    Returns:
      an operation which concatenates the string representations of all referenced single property values.
    Throws:
      `UnconvertibleObjectException` - if at least one of the given `singleAttributes` uses a value class which is not convertible from a `String`.
      `IllegalArgumentException` - if `singleAttributes` is an empty sequence, or contains a property which is neither an `AttributeType` or an `Operation` computing an attribute, or an attribute has a maximum number of occurrences greater than 1.
    See Also:
      - Compound key on Wikipedia

  - ### envelope

    public static AbstractOperation envelope(Map<String,?> identification, CoordinateReferenceSystem crs, AbstractIdentifiedType... geometryAttributes) throws FactoryException
    Creates an operation computing the envelope that encompass all geometries found in the given attributes. Geometries can be in different coordinate reference systems; they will be transformed to the first non-null CRS in the following choices:
    1. the CRS specified to this method,
    2. the CRS of the default geometry, or
    3. the CRS of the first non-empty geometry.
    The result of this operation is an `Attribute` with values of type `Envelope`. If the `crs` argument given to this method is non-null, then the envelope CRS will be that CRS.

    #### Limitations

    If a geometry contains other geometries, this operation queries only the envelope of the root geometry. It is the root geometry responsibility to take in account the envelope of all its children.

    #### Read/write behavior

    This operation is read-only. Calls to `Attribute​.setValue(Envelope)` will result in an `IllegalStateException` to be thrown.
    Warning: The type of `geometryAttributes` elements will be changed to `PropertyType` if and when such interface will be defined in GeoAPI.
    Parameters:
      `identification` - the name and other information to be given to the operation.
      `crs` - the Coordinate Reference System in which to express the envelope, or `null`.
      `geometryAttributes` - the operation or attribute type from which to get geometry values. Any element which is `null` or has a non-geometric value class will be ignored.
    Returns:
      an operation which will compute the envelope encompassing all geometries in the given attributes.
    Throws:
      `FactoryException` - if a coordinate operation to the target CRS can not be created.