FLINK基础139：DS流与表转换(5) Handling of (Insert-Only) Streams4toDataStream

The following code shows how to use toDataStream for different scenarios.

import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.table.api.DataTypes;
import org.apache.flink.table.api.Table;
import org.apache.flink.types.Row;
import java.time.Instant;

// POJO with mutable fields
// since no fully assigning constructor is defined, the field order
// is alphabetical [event_time, name, score]
public static class User {

    public String name;

    public Integer score;

    public Instant event_time;
}

tableEnv.executesql(
    "CREATE TABLE GeneratedTable "
    + "("
    + "  name STRING,"
    + "  score INT,"
    + "  event_time TIMESTAMP_LTZ(3),"
    + "  WATERMARK FOR event_time AS event_time - INTERVAL '10' SECOND"
    + ")"
    + "WITH ('connector'='datagen')");

Table table = tableEnv.from("GeneratedTable");


// === EXAMPLE 1 ===

// use the default conversion to instances of Row

// since `event_time` is a single rowtime attribute, it is inserted into the DataStream
// Metadata and watermarks are propagated

DataStream<Row> dataStream = tableEnv.toDataStream(table);


// === EXAMPLE 2 ===

// a data type is extracted from class `User`,
// the planner reorders fields and inserts implicit casts where possible to convert internal
// data structures to the desired structured type

// since `event_time` is a single rowtime attribute, it is inserted into the DataStream
// Metadata and watermarks are propagated

DataStream<User> dataStream = tableEnv.toDataStream(table, User.class);

// data types can be extracted reflectively as above or explicitly defined

DataStream<User> dataStream =
    tableEnv.toDataStream(
        table,
        DataTypes.STRUCTURED(
            User.class,
            DataTypes.FIELD("name", DataTypes.STRING()),
            DataTypes.FIELD("score", DataTypes.INT()),
            DataTypes.FIELD("event_time", DataTypes.TIMESTAMP_LTZ(3))));

Note that only non-updating tables are supported by toDataStream. Usually, time-based operations such as windows, interval joins, or the MATCH_RECOGNIZE clause are a good fit for insert-only pipelines next to simple operations like projections and filters.