How Can I Securely Parametrize IN Clauses in Android SQL Queries to Prevent SQL Injection?

Safe parameterized IN clause

In Android development, it is common for SQL queries to contain IN clauses using dynamic parameters. However, substituting parameters directly into the query can compromise security and lead to SQL injection vulnerabilities.

Challenge

The challenge is to safely parameterize the IN clause without compromising data integrity. Manually concatenating parameter values ​​into the query is unsafe and defeats the purpose of parameter binding, which is to prevent the accidental execution of malicious SQL commands.

Solution: Dynamic Question Mark

A safe solution involves dynamically generating a comma-separated string of question marks. This string can be embedded directly into the original SQL query, ensuring that the number of placeholders matches the number of parameters provided. Here's how it works:

1. Create a placeholder generator: Implement a function makePlaceholders(int len) that accepts the desired number of placeholders and returns a string containing that number of question marks (separated by commas).

2. Constructing a parameterized query: Compose a SQL query using the question mark string in the generated IN clause:

   <code>String query = "SELECT * FROM table WHERE name IN (" + makePlaceholders(names.length) + ")";</code>

3. Execute with parameters: Finally, the query is executed using the parameter binding method and the appropriate values ​​are provided as parameters.

Example implementation

The following is an example implementation of the makePlaceholders function:

String makePlaceholders(int len) {
    if (len < 1) {
        throw new IllegalArgumentException("Length must be at least 1");
    }
    StringBuilder sb = new StringBuilder(len * 2 - 1);
    sb.append("?");
    for (int i = 1; i < len; i++) {
        sb.append(",?");
    }
    return sb.toString();
}

By using this technique, you can safely parameterize the IN clause, thereby reducing the risk of SQL injection and ensuring the integrity of database operations.

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