Shuyi Chen created FLINK-9430:
---------------------------------
Summary: Support Casting of Object to Primitive types for Flink
SQL UDF
Key: FLINK-9430
URL: https://issues.apache.org/jira/browse/FLINK-9430
Project: Flink
Issue Type: New Feature
Components: Table API & SQL
Reporter: Shuyi Chen
Assignee: Shuyi Chen
We want to add a SQL UDF to access specific element in a JSON string using JSON
path. However, the JSON element can be of different types, e.g. Int, Float,
Double, String, Boolean and etc.. Since return type is not part of the method
signature, we can not use overload. So we will end up writing a UDF for each
type, e.g. GetFloatFromJSON, GetIntFromJSON and etc., which has a lot of
duplication.
One way to unify all these UDF functions is to implement one UDF and return
java.lang.Object, and in the SQL statement, use CAST AS to cast the returned
Object into the correct type. Below is an example:
{code:java}
object JsonPathUDF extends ScalarFunction {
def eval(jsonStr: String, path: String): Object = {
JSONParser.parse(jsonStr).read(path)
}
}{code}
{code:java}
SELECT CAST(jsonpath(json, "$.store.book.title") AS VARCHAR(32)) as bookTitle
FROM table1{code}
I have already got a local branch working. Please comment if there are
alternatives.
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