Short Description
    LookupJoin Attributes
    CTL Interface
    Java Interfaces
    Best Practices
    See also

    Short Description

    LookupJoin is a general purpose joiner. It merges potentially unsorted records from one data source incoming through the single input port with another data source from a lookup table based on a common key.

    ComponentSame input metadataSorted inputsSlave inputsOutputsOutput for drivers without slaveOutput for slaves without driverJoining based on equalityAuto-propagated metadata
    LookupJoin1 (virtual)1-2


    The joined data is then sent to the first output port.

    The second output port can optionally be used to capture unmatched master records.

    Port typeNumberRequiredDescriptionMetadata
    Input0Master input portAny
    1 (virtual)Slave input portAny
    Output0Output port for the joined dataAny

    Optional output port for master data records without slave matches. (Only if the Join type attribute is set to Inner join.) This applies only to LookupJoin and DBJoin.

    Input 0


    LookupJoin propagates metadata from the first input port to the second output port and from the second output port to the first input port. The propagation does not change the priority of metadata.

    LookupJoin has no metadata template.

    Either data source (input port and lookup table) may potentially have a different metadata structure.

    LookupJoin Attributes

    AttributeReqDescriptionPossible values
    Join keyyes

    Key according to which the incoming data flows are joined. See Join key.

    Left outer join 

    If set to true, also driver records without corresponding slave are parsed. Otherwise, inner join is performed.

    false (default) | true
    Lookup tableyes

    ID of the lookup table to be used as the resource of slave records.

    Number of lookup key fields and their data types must be the same as those of Join key. These fields values are compared and matched records are joined.

    Transform[1]Transformation in CTL or Java defined in the graph. 
    Transform URL[1]External file defining the transformation in CTL or Java. 
    Transform class[1]External transformation class. 
    Transform source charset 

    Encoding of the external file defining the transformation.

    The default encoding depends on DEFAULT_SOURCE_CODE_CHARSET in defaultProperties.

    E.g. UTF-8
    Clear lookup table after finishing 

    When set to true, memory caches of the lookup table will be emptied at the end of the execution of this component. This has different effects on different lookup table types.

    Simple lookup table and Range lookup table will contain 0 entries after this operation.

    For the other lookup table types, this will only erase cached data and therefore make more memory available, but the lookup table will still contain the same entries.

    false (default) | true
    Error actions 

    Definition of the action that should be performed when the specified transformation returns an Error code. See Return Values of Transformations.

    Error log 

    URL of the file to which error messages for specified Error actions should be written. If not set, they are written to Console.


    [1]  One of these must be set. These transformation attributes must be specified. Any of these transformation attributes must use a common CTL template for Joiners or implement a RecordTransform interface.


    LookupJoin is a general purpose joiner used in most common situations. It does not require the input to be sorted and is very fast as it is processed in memory.

    The data attached to the first input port is called the master, the second data source is called the slave. Its data is considered as if it were coming through the second (virtual) input port. Each master record is matched to the slave record on one or more fields known as the join key. The output is produced by applying a transformation which maps joined inputs to the output.

    Slave data is pulled out from a lookup table, so depending on the lookup table the data can be stored in the memory. This also depends on the lookup table type, e.g. Database lookup stores only the values which have already been queried. Master data is not stored in the memory.

    LookupJoin - how it works

    Figure 58.5. LookupJoin - how it works

    Join key

    Join key is a sequence of field names from the input metadata separated by a semicolon, colon or pipe. You can define the key in the Edit key wizard.

    Edit Key Wizard

    Figure 58.6. Edit Key Wizard

    A counterpart of this Join key of the input metadata is the key of lookup table in lookup tables. It is specified in the lookup table itself.

    Example 58.5. Join Key for LookupJoin


    This is the master part of fields that should serve to join master records with slave records.

    Lookup key should look like this:


    Corresponding fields will be compared and matching values will serve to join master and slave records.

    Key Duplicates in Lookup Table

    If the lookup table allows key duplicates, more output records can be created from a single input record.

    CTL Interface

    All Joiners share the same transformation template which can be found in CTL Templates for Joiners.

    Java Interfaces

    If you define your transformation in Java, it must implement the following interface that is common for all Joiners:

    Java Interfaces for Joiners

    See Public CloverDX API.


    Enrichment of Records Using Data from Lookup Table

    Given a list of number of customers for particular year per country with metadata fields CountryCode, Customers and Year.

    CZ |341 |2013
    CZE|417 |2014
    DE |2573|2013
    DE |3791|2014
    SK |457 |2014

    Replace the country code by country name. The list of country codes and corresponding country names is available from lookup table CountryCodeLookup.

    CZ |Czech Republic
    DE |Germany
    SK |Slovak Republic

    Use the attributes Join Key, Lookup Table and Transform.

    Join KeyCountryCode
    Lookup TableCountryCodeLookup
    TransformSee the code below.
    function integer transform() {
        $out.0.Customers = $in.0.Customers;
        $out.0.Country = $in.1.CountryName;
        $out.0.Year = $in.0.Year;
        return ALL;

    Values found in the lookup table are mapped in the same way as if they came from the second input port.

    The result records are

    Czech Republic |341 |2013
    Germany        |2573|2013
    Germany        |3791|2014
    Slovak Republic|457 |2014

    The country code CZE has not been found in the lookup table, so it has been sent unchanged to the second output port if an edge is connected.

    Matching Ranges with Range Lookup Table

    This example shows usage of Range Lookup Table table in LookupJoin.

    Records on the first data stream contains groups of accounts. Each group of accounts is defined by the lowest and highest account numbers, e.g. 12300 and 12399.

    Data on the second data stream contains account numbers. Match the accounts with groups.


    Load the records containing account ranges with LookupTableReaderWriter into Range Lookup Table.

    In the next phase, use LookupJoin to match the records from the second data stream.

    LookupJoin with Range Lookup Table

    Figure 58.7. LookupJoin with Range Lookup Table

    In LookupJoin set Join Key, Lookup Table, and Transform.

    Join KeyaccountNumber
    Lookup TableRangeLookupTable0
    TransformMap the fields that are necessary.

    Matching account into the ranges depends on the data type. If the account ranges and account number are specified as a whole number (integer/long), the records are compared as numbers. If the account ranges and account number are specified as a string, the records are compared as strings.

    If account numbers are integers (or longs) and the range is from 10 to 50, account 200 is out of the range.

    If account numbers are strings and the range is from 10 to 50, account 200 is within the range.

    Best Practices

    If the transformation is specified in an external file (with Transform URL), we recommend users to explicitly specify Transform source charset.