Dynamic expressions implementation

Question

I have one source table as :

S1       S2       S3       S4
 Hi      There    SSN1     SSN2 

where S1, S2, S3 and S4 are column names.

There is a target table likewise which has three fields:
T1 T2 T3

I have another table which is as follows:

Function            Target_Column
 concat(S1,S2)          T1
 substr(S3,1,3)         T2
 substr(S3,3,1)         T3 

I want to have such a mapping in which it can fetch the function name and map according to the function present in the table to the target column specified. My target table now after running the mapping will be:

T1         T2       T3
 HiThere   SSN       1

How can I achieve this?

Answer 1

Looks like you can use the Java API function invokeJExpression() inside Java transformation to derive the target columns.

(datatype)invokeJExpression(
String expression,
Object[] paramMetadataArray);
I guess the hard part would be to parse the concatenated string from your lookup to get the two parameters expression and paramMeradataArray

expression and paramMeradataArray should be something like below:

"concat(X1,X2)", [S1, S2]
"substr(X1,X2,X3)", [S1, 1, 3]
Note that you must start the parameters with X and number them consecutively.

Update:

Assuming from lookup you are getting the port lkp='concat(S1,S2)~T1::substr(S3,1,3)~T2::substr(S3,3,1)~T3', you can try the following code in Java transformation. However, this code might not work for all functions. For example, passing decimal values will not work.

Import Packages:

import java.util.regex.Matcher;
import java.util.regex.Pattern;
On Input Row:

String[] arr1 = lkp.split("::");

for (int i = 0; i < arr1.length; i++) {
    String[] arr2 = arr1[i].split("~");
    Pattern pattern = Pattern.compile("\\((.*?)\\)");
    Matcher matcher = pattern.matcher(arr2[0]);
    String params = "";
    if (matcher.find()) {
        params = matcher.group(1);
    }
    String[] param = params.split(",");
    Object[] args1 = new Object[param.length];
    String params1 = "";
    for (int j = 0; j < param.length; j++) {
        int index = j + 1;
        Object arg = new Object();
        params1 = params1 + (!params1.equals("") ? "," : "") + "X"
                + index;
        if (param[j].equals("S1"))
            arg = S1;
        else if (param[j].equals("S2"))
            arg = S2;
        else if (param[j].equals("S3"))
            arg = S3;
        else if (param[j].equals("S4"))
            arg = S4;
        else if (!param[j].startsWith("\'"))
            arg = Integer.parseInt(param[j]);
        else
            arg = param[j];
        args1[j] = arg;
    }

    String exp = matcher.replaceAll("(" + params1 + ")");
    if (arr2[1].equals("T1"))
        T1 = (String) invokeJExpression(exp, args1);
    else if (arr2[1].equals("T2"))
        T2 = (String) invokeJExpression(exp, args1);
    else if (arr2[1].equals("T3"))
        T3 = (String) invokeJExpression(exp, args1);

}