LookupField - CUBA Platform. Developer’s Manual

4.5.2.1.14. LookupField

This is a component to select a value from drop-down list. Drop-down list provides the filtering of values as the user inputs some text, and the pagination of available values.

XML name of the component: lookupField.

The LookupField component is implemented for Web Client and Desktop Client.

The simplest case of using LookupField is to select an enumeration value for an entity attribute. For example, a Role entity has a type attribute of the RoleType type, which is an enumeration. Then you can use LookupField to edit this attribute as follows:
```
<dsContext>
    <datasource id="roleDs" class="com.haulmont.cuba.security.entity.Role" view="_local"/>
</dsContext>
<layout>
    <lookupField datasource="roleDs" property="type"/>
```
In the example above, the screen defines roleDs data source for the Role entity. In the lookupField component, a link to a data source is specified in the datasource attribute, and a name of an entity attribute is specified in the property attribute. In this case, the entity attribute is an enumeration and the drop-down list will display localized names of all enumeration values.
Similarly, LookupField can be used to select an instance of a related entity. optionsDatasource attribute is used to create a list of options:
```
<dsContext>
    <datasource id="carDs" class="com.company.sample.entity.Car" view="_local"/>
    <collectionDatasource id="coloursDs" class="com.company.sample.entity.Colour" view="_local">
        <query>select c from sample$Colour c</query>
    </collectionDatasource>
</dsContext>
<layout>
    <lookupField datasource="carDs" property="colour" optionsDatasource="coloursDs"/>
```
In this case, the component will display instance names of the Colour entity located in the colorsDs data source, and the selected value will be set into the colour attribute of the Car entity, which is located in the carDs data source.

captionProperty attribute defines which entity attribute can be used instead of an instance name for string option names.
The list of component options can be specified arbitrarily using the setOptionsList(), setOptionsMap() and setOptionsEnum() methods, or using the XML optionsDatasource attribute.
- setOptionsList() allows you to programmatically specify a list of component options. To do this, declare a component in the XML descriptor:
  <lookupField id="numberOfSeatsField" datasource="modelDs" property="numberOfSeats"/>
  Then inject the component into the controller and specify a list of options in the init() method:
  @Inject protected LookupField numberOfSeatsField; @Override public void init(Map<String, Object> params) { List<Integer> list = new ArrayList<>(); list.add(2); list.add(4); list.add(5); list.add(7); numberOfSeatsField.setOptionsList(list); }
  In the component’s drop-down list the values 2, 4, 5 and 7 will be displayed. Selected number will be put into the numberOfSeats attribute of an entity located in the modelDs data source.
- setOptionsMap() allows you to specify string names and option values separately. For example, in the numberOfSeatsField component in the XML descriptor, specify an option map in init():
  @Inject protected LookupField numberOfSeatsField; @Override public void init(Map<String, Object> params) { Map<String, Object> map = new LinkedHashMap<>(); map.put("two", 2); map.put("four", 4); map.put("five", 5); map.put("seven", 7); numberOfSeatsField.setOptionsMap(map); }
  In the component’s drop-down list, two, four, five, seven strings will be displayed. However, the value of the component will be a number that corresponds to the selected option. It will be put into the numberOfSeats attribute of an entity located in the modelDs data source.
- setOptionsEnum() takes the class of an enumeration as a parameter. The drop-down list will show localized names of enum values, the value of the component will be an enum value.

Using the filterMode attribute, option filtering type can be defined for the user input:
- NO − no filtering.
- STARTS_WITH − by the beginning of a phrase.
- CONTAINS − by any occurrence (is used by default).
If the LookupField component is not required and if the related entity attribute is not declared as required, the list of component options has an empty row. If this row is selected, the component returns null. The nullName attribute allows you to specify a row to be displayed in this case instead of an empty one. Below is an example:
```
<lookupField datasource="carDs" property="colour" optionsDatasource="coloursDs" nullName="(none)"/>
```
In this case, instead of an empty row, (none) will be displayed. If this row is selected, null will be set to a related entity attribute.

If you specify a list of options programmatically using setOptionsList(), you can pass one of the options into setNullOption() method. Then, if the user selects it, the component value will be null.
The LookupField component is able to handle user input if there is no suitable option in the list. In this case, setNewOptionAllowed() and setNewOptionHandler() are used. For example:
```
@Inject
protected LookupField colourField;

@Inject
protected CollectionDatasource<Colour, UUID> coloursDs;

@Override
public void init(Map<String, Object> params) {
    colourField.setNewOptionAllowed(true);
    colourField.setNewOptionHandler(new LookupField.NewOptionHandler() {
        @Override
        public void addNewOption(String caption) {
            Colour colour = new Colour();
            colour.setName(caption);
            coloursDs.addItem(colour);
            colourField.setValue(colour);
        }
    });
}
```
The NewOptionHandler handler is invoked if the user enters a value that does not coincide with any option and presses Enter. In this case, a new Colour entity instance is created in the handler, its name attribute is set to the value entered by the user, this instance is added to the options data source and selected in the component.

Instead of implementing the LookupField.NewOptionHandler interface for processing user input, the controller method name can be specified in the newOptionHandler XML-attribute. This method should have two parameters, one of LookupField type, and the other of String type. They will be set to the component instance and the value entered by the user, accordingly. The newOptionAllowed attribute is used to enable adding new options instead of the setNewOptionAllowed() method.

The textInputAllowed XML attribute can be used to disable filtering options from keyboard. It can be convenient for short lists. The default value is true.

The pageLength XML attribute allows you to redefine the number of options on one page of the drop-down list, specified in the cuba.gui.lookupFieldPageLength application property.

Attributes of lookupField: align - caption - captionProperty - datasource - description - editable - enable - filterMode - height - icon - id - inputPrompt - newOptionAllowed - newOptionHandler - nullName - optionsDatasource - pageLength - property - required - requiredMessage - stylename - textInputAllowed - visible - width
Elements of lookupField: validator