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## CheckForeignKey

# Not available in Community Designer

Short Description
Ports
Metadata
CheckForeignKey Attributes
Details
Examples
See also

### Short Description

CheckForeignKey checks the validity of foreign key values and replaces invalid values by valid ones.

Component | Same input metadata | Sorted inputs | Inputs | Outputs | Each to all outputs | Java | CTL | Auto-propagated metadata
--- | --- | --- | --- | --- | --- | --- | --- | ---
CheckForeignKey | - |  | 2 | 1-2 | - |  |  |

### Icon

### Ports

Port type | Number | Required | Description | Metadata
--- | --- | --- | --- | ---
Input | 0 |  | For data with foreign key | Any1
1 |  | For data with primary key | Any2
Output | 0 |  | For data with corrected key | Input 0
1 |  | For data with invalid key | Input 0

### Metadata

Metadata cannot be propagated through this component.

CheckForeignKey has no metadata template.

Metadata on both input ports can be different. Metadata on the output(s) are usually the same as those on the first input port. They must at least have the same metadata structure (the number of fields, data types and sizes). Field names may differ.

### CheckForeignKey Attributes

Attribute | Req | Description | Possible values
--- | --- | --- | ---
Basic
Foreign key | yes | Key that is compared according to which both incoming data flows are compared and data records are distributed among different output ports. See Foreign Key for more information. |
Default foreign key | yes | Sequence of values corresponding to the Foreign key data types separated from each other by semicolon. Serves to replace invalid foreign key values. See Foreign Key for more information. |
Equal NULL |  | By default, records with null values of fields are considered to be different. If set to `true`, nulls are considered to be equal. | false (default) | true
Advanced
Hash table size |  | Table for storing key values. Should be higher than the number of records with unique key values. | 512 (default) | properties
Deprecated
Primary key |  | Sequence of field names from the second input port separated from each other by semicolon. See Deprecated: Primary Key for more information. |

### Details

CheckForeignKey receives data records through two input ports.

The data records on the first input port are compared with those one the second input port. If some value of the specified foreign key (input port 0) is not found within the values of the primary key (input port1), default value is given to the foreign key instead of its invalid value. Then all of the foreign records are sent to the first output port with the new (corrected) foreign key values and the original foreign records with invalid foreign key values can be sent to the optional second output port if it is connected.

#### Foreign Key

The Foreign key is a sequence of individual assignments separated from each other by semicolon. Each of these individual assignments looks like this: `$foreignField=$primaryKey`.

To define Foreign key, you must select the desired fields in the Foreign key tab of the Foreign key definition wizard. Select the fields from the Fields pane on the left and move them to the Foreign key pane on the right.

Figure 56.1. Foreign Key Definition Wizard (Foreign Key Tab)

When you switch to the Primary key tab, you will see that the selected foreign fields appeared in the Foreign key column of the Foreign key definition pane.

Figure 56.2. Foreign Key Definition Wizard (Primary Key Tab)

You only need to select some primary fields from the left pane and move them to the Primary key column of the Foreign key definition pane on the right.

Figure 56.3. Foreign Key Definition Wizard (Foreign and Primary Keys Assigned)

You must also define the default foreign key values (Default foreign key). This key is also a sequence of values of corresponding data types separated from each other by semicolon. The number and data types must correspond to metadata of the foreign key.

If you want to define the default foreign key values, you need to click the Default foreign key attribute row and type the default values for all fields.

#### Deprecated: Primary Key

In older versions of Clover you had to specify both the primary and the foreign keys using the Primary key and the Foreign key attributes, respectively. They had the form of a sequence of field names separated from each other by semicolon. However, the use of Primary key is deprecated now.

### Examples

#### Checking City Names of Branch Offices

Check list of customers for cities without our branch office.

List of customers

    John Doe        | London
    Lucy Brown      | Glasgow
    Elisabeth Smith | Stratford-upon-Avon
    ...

List of cities with our branch office

    Edinburgh
    Glasgow
    London
    ...

##### Solution

Pass list of customers (CustomerName and BranchOfficeCity) to the first input port and list of cities with branch offices to the second input port.

Use Foreign key and Default foreign key attributes.

Attribute | Value
--- | ---
Foreign key | $BranchOfficeCity=$city
Default foreign key | Not Found;

If city from the list of customers was not found in the list with branch office cities, we changed city name to Not Found.

### See also

Common Properties of Components
Specific Attribute Types
Others Comparison

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