User Defined Function Data Type incompatability

Neo4j Graph Platform Procedures & APOC
1

I'm trying to create a user defined procedure and it compiles okay but Neo4j fails to re-start after introducing the jar file. I'm trying to convert a string of 0's and 1's representing a base 2 number to a base 10 number which is returned as a long integer. I don't understand how to get the long output required by Neo4j. The error message in the log file is:

Caused by: org.neo4j.internal.kernel.api.exceptions.ProcedureException: Argument radix at position 1 in baseConvert with type Integer cannot be converted to a Neo4j type: Don't know how to map java.lang.Integer to the Neo4j Type System.

The code is:

package genealogy;
import org.neo4j.procedure.Description;
import org.neo4j.procedure.Name;
import org.neo4j.procedure.UserFunction;

/**
 * This is an example of a simple user-defined function for Neo4j to perform a baseConvert
 */
public class base2to10 {

    @UserFunction
    @Description("example.baseConvert('1101', 2) - Convert the provided base 2 string to a base 10 integer.")
    public Integer baseConvert(
            @Name("s") 
                String s,
            @Name(value = "radix") 
                Integer radix
            ) 
    {
        if (s == null || radix == null) {
            return null;
        }
        return Integer.parseInt(s, radix);
    }
}
2

Need to use Long in place of Integer.

I ran into the same thing yesterday evening and was eventually able to resolve by changing the type. The documentation does include a type mapping entry, but it wasn't immediately obvious in the udf section.

Values and types - Neo4j Java Reference

1 Like
3

Mike,

Thanks! So others can see the full final solutions ...

package genealogy;
import org.neo4j.procedure.Description;
import org.neo4j.procedure.Name;
import org.neo4j.procedure.UserFunction;

/**
 * This is an example of a simple user-defined function for Neo4j to perform a baseConvert
 */
public class base2to10 {

    @UserFunction
    @Description("example.baseConvert('1101', 2) - Convert the provided base 2 string to a base 10 integer.")
    public Long baseConvert(
            @Name("s") 
                String s
            
            ) 
    {
       
        return Long.parseLong(s,  2);
    }
}

I'm only working with base 2 to produce ahnentafel numbers ....

Then

return genealogy.baseConvert('111101')

produces
61

1 Like