Concatenating Strings in XQuery with `concat()`: A Practical Guide

Master string concatenation in XQuery using the `concat()` function. This tutorial explains its syntax, demonstrates its use with various string arguments, and provides practical examples showing how to combine strings for data manipulation and transformation within your XQuery expressions.

Concatenating Strings in XQuery with `concat()`

Understanding `concat()`

The XQuery `concat()` function joins multiple strings together into a single string. This function is fundamental for string manipulation in XQuery, offering a simple and efficient way to combine string values. The strings to be concatenated are passed as arguments to the `concat()` function, and the combined string is returned as the result.

`concat()` Syntax

The syntax is:

concat($string1 as xs:anyAtomicType?, $string2 as xs:anyAtomicType?, ... ) as xs:string

It takes one or more string arguments and returns a single string.

Example: Concatenating a Book Title and Price

This example demonstrates using `concat()` in an XQuery expression. The XQuery code retrieves a book title and concatenates it with a price string. This simple example shows how to concatenate strings using the XQuery `concat()` function. The Java code executes this XQuery expression, which combines the title and price.

1. XQuery Code (`books.xqy`)

let $bookTitle := "Learn XQuery in 24 hours"
let $updatedTitle := concat($bookTitle, ", price: $200")
return $updatedTitle

2. Java Code (`XQueryTester.java`)

This Java code uses the Saxon library to execute the XQuery. You'll need to have the Saxon JAR files in your classpath for this code to run correctly. The Java code handles reading and executing the XQuery expression. The output will be the result of the `concat()` operation.

import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import javax.xml.xquery.*;
import com.saxonica.xqj.SaxonXQDataSource;

public class XQueryTester {
    public static void main(String[] args) {
        try {
            execute();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    // ... execute() method ...
}

private static void execute() throws Exception {
    InputStream inputStream = new FileInputStream(new File("books.xqy"));
    XQDataSource ds = new SaxonXQDataSource();
    XQConnection conn = ds.getConnection();
    XQPreparedExpression exp = conn.prepareExpression(inputStream);
    XQResultSequence result = exp.executeQuery();
    while (result.next()) {
        System.out.println(result.getItemAsString(null));
    }
}

Conclusion

The XQuery `concat()` function is a fundamental string manipulation function. It's widely used to combine strings, creating more complex text values. It's essential for tasks such as building customized output strings based on data extracted from XML documents.