Scala UDF handler examples

This topic includes simple examples of UDF handler code written in Scala.

For information on using Scala to create a scalar UDF handler, refer to Writing a scalar UDF in Scala. For general coding guidelines, refer to General Scala UDF handler coding guidelines.

Creating and calling a simple in-line Scala UDF

The following statements create and call an in-line Scala UDF. This code returns the VARCHAR passed to it.

This function is declared with the optional CALLED ON NULL INPUT clause to indicate that the function is called even if the value of the input is NULL. (This function would return NULL with or without this clause, but you could modify the code to handle NULL another way, for example, to return an empty string.)

Create the UDF

CREATE OR REPLACE FUNCTION echo_varchar(x VARCHAR)
RETURNS VARCHAR
LANGUAGE SCALA
CALLED ON NULL INPUT
RUNTIME_VERSION = 2.12
HANDLER='Echo.echoVarchar'
AS
$$
class Echo {
  def echoVarchar(x : String): String = {
    return x
  }
}
$$;
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Call the UDF

SELECT echo_varchar('Hello');
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Passing a NULL to an in-line Scala UDF

This uses the echo_varchar() UDF defined above. The SQL NULL value is implicitly converted to Scala Null, and that Scala Null is returned and implicitly converted back to SQL NULL:

Call the UDF:

SELECT echo_varchar(NULL);
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Returning NULL explicitly from an in-line UDF

The following code shows how to return a NULL value explicitly. The Scala value Null is converted to SQL NULL.

Create the UDF

CREATE OR REPLACE FUNCTION return_a_null()
RETURNS VARCHAR
LANGUAGE SCALA
RUNTIME_VERSION = 2.12
HANDLER='TemporaryTestLibrary.returnNull'
AS
$$
class TemporaryTestLibrary {
  def returnNull(): String = {
    return null
  }
}
$$;
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Call the UDF

SELECT return_a_null();
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Passing an OBJECT to an in-line Scala UDF

The following example uses the SQL OBJECT data type and the corresponding Scala data type (Map[String, String]), and extracts a value from the OBJECT. This example also shows that you can pass multiple parameters to a Scala UDF.

Create and load a table that contains a column of type OBJECT:

CREATE TABLE objectives (o OBJECT);
INSERT INTO objectives SELECT PARSE_JSON('{"outer_key" : {"inner_key" : "inner_value"} }');
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Create the UDF

CREATE OR REPLACE FUNCTION extract_from_object(x OBJECT, key VARCHAR)
RETURNS VARIANT
LANGUAGE SCALA
RUNTIME_VERSION = 2.12
HANDLER='VariantLibrary.extract'
AS
$$
import scala.collection.immutable.Map

class VariantLibrary {
  def extract(m: Map[String, String], key: String): String = {
    return m(key)
  }
}
$$;
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Call the UDF

SELECT extract_from_object(o, 'outer_key'),
  extract_from_object(o, 'outer_key')['inner_key'] FROM OBJECTIVES;
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Passing an ARRAY to an in-line Scala UDF

The following example uses the SQL ARRAY data type.

Create the UDF

CREATE OR REPLACE FUNCTION generate_greeting(greeting_words ARRAY)
RETURNS VARCHAR
LANGUAGE SCALA
RUNTIME_VERSION = 2.12
HANDLER='StringHandler.handleStrings'
AS
$$
class StringHandler {
  def handleStrings(strings: Array[String]): String = {
    return concatenate(strings)
  }
  private def concatenate(strings: Array[String]): String = {
    var concatenated : String = ""
    for (newString <- strings)  {
        concatenated = concatenated + " " + newString
    }
    return concatenated
  }
}
$$;
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Reading a file with a Scala UDF

You can read the contents of a file with handler code. For example, you might want to read a file to process unstructured data with the handler.

The file must be on a Snowflake stage that’s available to your handler.

To read the contents of staged files, your handler can read a dynamically-specified file by calling methods of either the SnowflakeFile class or the InputStream class.

You might do this if you need to access a file specified by the caller. For more information, see the following in this topic:

SnowflakeFile provides features not available with InputStream, as described in the following table.

Class

Input

Notes

SnowflakeFile

URL formats:

  • Scoped URL to reduce the risk of file injection attacks when the function’s caller is not also its owner.

  • File URL or string path for files that the UDF owner has access to.

The file must be located in a named internal stage or an external stage.

Easily access additional file attributes, such as file size.

InputStream

URL formats:

  • Scoped URL to reduce the risk of file injection attacks when the function’s caller is not also its owner.

The file must be located in a named internal stage or an external stage.

Note

The UDF owner must have access to any files whose locations are not scoped URLs. You can read these staged files by having the handler code call the SnowflakeFile.newInstance method with a boolean value for a new requireScopedUrl parameter.

The following example uses SnowflakeFile.newInstance while specifying that a scoped URL is not required.

var filename = "@my_stage/filename.txt"
var sfFile = SnowflakeFile.newInstance(filename, false)
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Reading a dynamically-specified file with SnowflakeFile

Using methods of the SnowflakeFile class, you can read files from a stage with your handler code. The SnowflakeFile class is included on the classpath available to Scala UDF handlers on Snowflake.

Note

To make your code resilient to file injection attacks, always use a scoped URL when passing a file’s location to a UDF, particularly when the function’s caller is not also its owner. You can create a scoped URL in SQL using the built-in function BUILD_SCOPED_FILE_URL. For more information about what the BUILD_SCOPED_FILE_URL does, see Introduction to unstructured data.

To develop your UDF code locally, add the Snowpark JAR containing SnowflakeFile to your code’s class path. For information about snowpark.jar, see Setting Up Your Development Environment for Snowpark Scala. Note that Snowpark client applications cannot use this class.

When you use SnowflakeFile, it isn’t necessary to also specify either the staged file or the JAR containing SnowflakeFile with an IMPORTS clause when you create the UDF, as in SQL with a CREATE FUNCTION statement.

Create the UDF

Code in the following example uses SnowflakeFile to read a file from a specified stage location. Using an InputStream from the getInputStream method, it reads the file’s contents into a String variable.

CREATE OR REPLACE FUNCTION sum_total_sales_snowflake_file(file string)
RETURNS INTEGER
LANGUAGE SCALA
RUNTIME_VERSION = 2.12
PACKAGES=('com.snowflake:snowpark:latest')
HANDLER='SalesSum.sumTotalSales'
AS
$$
import java.io.InputStream
import java.io.IOException
import java.nio.charset.StandardCharsets
import com.snowflake.snowpark_java.types.SnowflakeFile

object SalesSum {
  @throws(classOf[IOException])
  def sumTotalSales(filePath: String): Int = {
    var total = -1

    // Use a SnowflakeFile instance to read sales data from a stage.
    val file = SnowflakeFile.newInstance(filePath)
    val stream = file.getInputStream()
    val contents = new String(stream.readAllBytes(), StandardCharsets.UTF_8)

    // Omitted for brevity: code to retrieve sales data from JSON and assign it to the total variable.

    return total
  }
}
$$;
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Call the UDF

SELECT sum_total_sales_input_stream(BUILD_SCOPED_FILE_URL('@sales_data_stage', '/car_sales.json'));
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Reading a dynamically-specified file with InputStream

You can read file contents directly into a java.io.InputStream by making your handler function’s argument an InputStream variable. This can be useful when the function’s caller will want to pass a file path as an argument.

Note

To make your code resilient to file injection attacks scoped URLs are required when passing a file’s location to a UDF. You can create a scoped URL in SQL using the built-in function BUILD_SCOPED_FILE_URL. For more information about what the BUILD_SCOPED_FILE_URL does, see Introduction to unstructured data.

Create the UDF

Code in the following example has a handler function sumTotalSales that takes an InputStream and returns an Int. At run time, Snowflake automatically assigns the contents of the file at the file variable’s path to the stream argument variable.

CREATE OR REPLACE FUNCTION sum_total_sales_input_stream(file STRING)
RETURNS NUMBER
LANGUAGE SCALA
RUNTIME_VERSION = 2.12
HANDLER = 'SalesSum.sumTotalSales'
PACKAGES = ('com.snowflake:snowpark:latest')
AS $$
import com.snowflake.snowpark.types.Variant
import java.io.InputStream
import java.io.IOException
import java.nio.charset.StandardCharsets
object SalesSum {
  @throws(classOf[IOException])
  def sumTotalSales(stream: InputStream): Int = {
    val total = -1
    val contents = new String(stream.readAllBytes(), StandardCharsets.UTF_8)

    // Omitted for brevity: code to retrieve sales data from JSON and assign it to the total variable.

    return total
  }
}
$$;
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Call the UDF

SELECT sum_total_sales_input_stream(BUILD_SCOPED_FILE_URL('@sales_data_stage', '/car_sales.json'));
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