[GitHub] [flink] wuchong commented on a change in pull request #10096: [FLINK-14623][table-api] Add computed column information into TableSc…

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wuchong commented on a change in pull request #10096: [FLINK-14623][table-api] Add computed column information into TableSc…
URL: https://github.com/apache/flink/pull/10096#discussion_r343098831
 
 

 ##########
 File path: flink-table/flink-table-common/src/main/java/org/apache/flink/table/api/TableColumn.java
 ##########
 @@ -0,0 +1,131 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.table.api;
+
+import org.apache.flink.annotation.PublicEvolving;
+import org.apache.flink.table.types.DataType;
+import org.apache.flink.util.Preconditions;
+
+import javax.annotation.Nullable;
+
+import java.util.Objects;
+import java.util.Optional;
+
+/**
+ * A table column represents a table column's structure with
+ * column name, column data type and computation expression(if it is a computed column).
+ */
+@PublicEvolving
+public class TableColumn {
+
+	//~ Instance fields --------------------------------------------------------
+
+	private final String name;
+	private final DataType type;
+	@Nullable
+	private final String expr;
+
+	//~ Constructors -----------------------------------------------------------
+
+	/**
+	 * Creates a {@link TableColumn} instance.
+	 *
+	 * @param name Column name
+	 * @param type Column data type
+	 * @param expr Column computation expression if it is a computed column
+	 */
+	private TableColumn(
+			String name,
+			DataType type,
+			@Nullable String expr) {
+		this.name = name;
+		this.type = type;
+		this.expr = expr;
+	}
+
+	//~ Methods ----------------------------------------------------------------
+
+	/**
+	 * Creates a table column from given name and data type.
+	 */
+	public static TableColumn of(String name, DataType type) {
+		Preconditions.checkNotNull(name, "Column name can not be null!");
+		Preconditions.checkNotNull(type, "Column type can not be null!");
+		return new TableColumn(
+			name,
+			type,
+			null);
+	}
+
+	/**
+	 * Creates a table column from given name and computation expression.
+	 *
+	 * @param name Name of the column
+	 * @param expression SQL-style expression
+	 */
+	public static TableColumn of(String name, DataType type, String expression) {
+		Preconditions.checkNotNull(name, "Column name can not be null!");
+		Preconditions.checkNotNull(type, "Column type can not be null!");
+		Preconditions.checkNotNull(expression, "Column expression can not be null!");
+		return new TableColumn(name, type, expression);
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (this == o) {
+			return true;
+		}
+		if (o == null || getClass() != o.getClass()) {
+			return false;
+		}
+		TableColumn that = (TableColumn) o;
+		return Objects.equals(this.name, that.name)
+			&& Objects.equals(this.type, that.type)
+			&& Objects.equals(this.expr, that.expr);
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(this.name, this.type, this.expr);
+	}
+
+	//~ Getter/Setter ----------------------------------------------------------
+
+	public DataType getType() {
+		return this.type;
+	}
+
+	public String getName() {
+		return name;
+	}
+
+	public Optional<String> getExpr() {
 
 Review comment:
   We should align this method name and `WatermarkSpec#getExpressionString`. 
   From my point of view, I would prefer `getExpressionString` because "method name is the best documentation".

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