Version

    Multivalue Fields

    Lists and Maps Support in Components
    Joining on Lists and Maps (Comparison Rules)

    Each metadata field commonly stores only one value, e.g. one integer, one string, one date, etc. However, you can also set one field to carry more values of the same type.

    [Note]Note

    Multivalue fields is a new feature available as of version 3.3.

    Example 31.3. Example situations when you could take advantage of multivalue fields

    • A record containing an employee's ID, Name and Address. Since employees move from time to time, you might need to keep track of all their addresses, both current and past. Instead of creating new metadata fields each time an employee moves to a new address, you can store a list of all addresses into one field.

    • You are processing an input stream of CSV files, each containing a different column count. Normally, that would imply creating new metadata for each file (each column count). Instead, you can define a generic map in metadata and append fields to it each time they occur.


    As implied above, there are two types of structures:

    list - is a set containing elements of a given data type (any you want). In source code, lists are marked by the [] brackets, for example: 

    integer[] list1 = [1, 367, -1, 20, 5, 0, -79]; // a list of integer elements
boolean[] list2 = [true, false, randomBoolean()]; // a list of three boolean elements
string[] list3; // a just-declared empty list to be filled by strings

    map - is a pair of keys and their values. A key is always a string while a value can be any data type - but you cannot mix them (remember a map holds values of the same type). Example: 

    map[string,date] dateMap; // declaration

// filling the map with values
dateMap["a"] = 2011-01-01;
dateMap["b"] = 2012-12-31;
dateMap["c"] = randomDate(2011-01-01,2012-12-31);

    For more information about maps and lists, see Data Types in CTL2.

    [Important]Important

    To change a field from single-value to multi-value:

    1. Go to Metadata Editor.

    2. Click a field or create a new one.

    3. In Property → Basic, switch Container Type either to list or map. (You will see an icon appears next to the field Type in the left hand record pane.)

    Lists and Maps Support in Components

    An alphabetically sorted list of components which you can use multivalue fields in:

    ComponentListMapNote
    CloverDataReader
    yes
    yes
    		 
    CloverDataWriter
    yes
    yes
    		 
    ParallelSimpleGatheryesyesRound robin
    yesnoMerge by key
    yesyesSimple gather
    ParallelPartitionnonoRanges
    yesnoPartition key
    yesyesPartition class
    Concatenate
    yes
    yes
    		 
    DataGenerator
    yes
    yes
    		 
    DataIntersection
    yes
    		no 
    yes
    		yesMap is not a part of key
    DBJoin
    yes
    yes
    		Map is not a part of key
    Dedup
    yes
    		no 
    yes
    		yesMap is not a part of key
    Denormalizer
    yes
    		no 
    yes
    		yesMap is not a part of key
    Filter
    yes
    yes
    		 
    ExtHashJoin
    yes
    		no 
    yes
    		yesMap is not a part of key
    ExtMergeJoin
    yes
    yes
    		Map is not a part of key
    ExtSort
    yes
    		no 
    yes
    		yesMap is not a part of key.
    JavaBeanReader
    yes
    		no 
    JavaBeanWriter
    yes
    		no 
    JavaMapWriter
    yes
    yes
    		 
    JSONExtract
    yes
    		no 
    JSONReader
    yes
    		no 
    JSONWriter
    yes
    		no 
    LookupJoin
    yes
    yes
    		 
    LookupTableReaderWriter
    yes
    yes
    		 
    Merge
    yes
    		no 
    yes
    		yesMap is not a part of key
    Normalizer
    yes
    		no 
    yes
    		yesMap is not a part of key
    PartitionnonoRanges
    yesnoPartition key
    yesyesPartition class
    Reformat
    yes
    yes
    		 
    RelationalJoin
    yes
    yes
    		Map is not a part of key
    RollupyesnoSorted input
    yesyesSorted input, map not part of key
    yesyesUnsorted input
    SequenceChecker
    yes
    		no 
    yes
    		yesMap is not a part of key
    SimpleCopy
    yes
    yes
    		 
    SimpleGather
    yes
    yes
    		 
    Sleep
    yes
    yes
    		 
    SortWithinGroups
    yes
    		no 
    XMLExtract
    yes
    		no 
    XMLReader
    yes
    		no 
    XMLWriter
    yes
    yes
    		 

    At the moment, neither map nor list structures can be extracted as metadata from flat files.

    Joining on Lists and Maps (Comparison Rules)

    You can specify fields that are lists or maps as Join keys (see Join Types) just like any other fields. The only question is when two maps (lists) equal.

    A list/map can:

    Two maps (lists) are equal if both of them are not null, they have the same data type, element count and all element values (keys-values in maps) are equal.

    Two maps (lists) are not equal if either of them is null.

    [Important]Important

    When comparing two lists, the order of their elements has to match, too. In maps, there is no 'order' of elements, therefore you cannot use them in Sort key.

    Example 31.4. Integer lists which are (not) equal - symbolic notation

    [1,2] == [1,2]
[null] != [1,2]
[1] != [1,2]
null != null // two unspecified lists
[null] == [null] // an extra case: lists which are not empty but whose elements are null

    Note: Maps are implemented as LinkedHashMap, thus their properties derive from it.