[GitHub] [iceberg] openinx commented on a change in pull request #2010: Core: Add primary key spec.

[GitBox <gi...@apache.org>]

openinx commented on a change in pull request #2010:
URL: https://github.com/apache/iceberg/pull/2010#discussion_r551175643



##########
File path: api/src/main/java/org/apache/iceberg/PrimaryKey.java
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@@ -0,0 +1,221 @@
+/*
+ * 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.iceberg;
+
+import java.io.Serializable;
+import java.util.Arrays;
+import java.util.List;
+import org.apache.iceberg.exceptions.ValidationException;
+import org.apache.iceberg.relocated.com.google.common.base.MoreObjects;
+import org.apache.iceberg.relocated.com.google.common.base.Preconditions;
+import org.apache.iceberg.relocated.com.google.common.collect.ImmutableList;
+import org.apache.iceberg.relocated.com.google.common.collect.Lists;
+import org.apache.iceberg.types.Type;
+import org.apache.iceberg.types.Types;
+
+/**
+ * A primary key that defines which columns will be unique in this table.
+ */
+public class PrimaryKey implements Serializable {
+
+  private static final PrimaryKey NON_PRIMARY_KEY = new PrimaryKey(null, 0, false, ImmutableList.of());
+
+  private final Schema schema;
+  private final int keyId;
+  private final boolean enforceUniqueness;
+  private final Integer[] sourceIds;
+
+  private transient volatile List<Integer> sourceIdList;
+
+  private PrimaryKey(Schema schema, int keyId, boolean enforceUniqueness, List<Integer> sourceIds) {
+    this.schema = schema;
+    this.keyId = keyId;
+    this.enforceUniqueness = enforceUniqueness;
+    this.sourceIds = sourceIds.toArray(new Integer[0]);
+  }
+
+  /**
+   * Returns the {@link Schema} for this primary key.
+   */
+  public Schema schema() {
+    return schema;
+  }
+
+  /**
+   * Returns this ID of this primary key.
+   */
+  public int keyId() {
+    return keyId;
+  }
+
+  /**
+   * Returns true if the uniqueness should be guaranteed when writing iceberg table.
+   */
+  public boolean enforceUniqueness() {
+    return enforceUniqueness;
+  }
+
+  /**
+   * Returns the list of source field ids for this primary key.
+   */
+  public List<Integer> sourceIds() {
+    if (sourceIdList == null) {
+      synchronized (this) {
+        if (sourceIdList == null) {
+          this.sourceIdList = ImmutableList.copyOf(sourceIds);
+        }
+      }
+    }
+    return sourceIdList;
+  }
+
+  /**
+   * Returns true if the primary key has no column.
+   */
+  public boolean isNonPrimaryKey() {
+    return sourceIds.length == 0;
+  }
+
+  /**
+   * Returns a dummy primary key that has no column.
+   */
+  public static PrimaryKey nonPrimaryKey() {
+    return NON_PRIMARY_KEY;
+  }
+
+  /**
+   * Checks whether this primary key is equivalent to another primary key while ignoring the primary key id.
+   *
+   * @param other a different primary key.
+   * @return true if this key is equivalent to the given key.
+   */
+  public boolean samePrimaryKey(PrimaryKey other) {
+    return Arrays.equals(sourceIds, other.sourceIds) && enforceUniqueness == other.enforceUniqueness;
+  }
+
+  @Override
+  public boolean equals(Object other) {
+    if (this == other) {
+      return true;
+    } else if (!(other instanceof PrimaryKey)) {
+      return false;
+    }
+
+    PrimaryKey that = (PrimaryKey) other;
+    if (this.keyId != that.keyId) {
+      return false;
+    }
+
+    if (this.enforceUniqueness != that.enforceUniqueness) {
+      return false;
+    }
+
+    return Arrays.equals(sourceIds, that.sourceIds);
+  }
+
+  @Override
+  public int hashCode() {
+    int hash = 31 * keyId;
+    hash = hash + (enforceUniqueness ? 1 : 0);
+    hash += Arrays.hashCode(sourceIds);
+    return hash;
+  }
+
+  @Override
+  public String toString() {
+    return MoreObjects.toStringHelper(this)
+        .add("keyId", keyId)
+        .add("enforceUniqueness", enforceUniqueness)
+        .add("sourceIds", sourceIds())
+        .toString();
+  }
+
+  /**
+   * Creates a new {@link Builder primary key builder} for the given {@link Schema}.
+   *
+   * @param schema a schema
+   * @return a primary key builder for the given schema.
+   */
+  public static Builder builderFor(Schema schema) {
+    return new Builder(schema);
+  }
+
+  /**
+   * A builder to create valid {@link PrimaryKey primary keys}. Call {@link #builderFor(Schema)} to create a new
+   * builder.
+   */
+  public static class Builder {
+    private final Schema schema;
+    private final List<Integer> sourceIds = Lists.newArrayList();
+    // Default ID to 1 as 0 is reserved for non primary key.
+    private int keyId = 1;
+    private boolean enforceUniqueness = false;
+
+    private Builder(Schema schema) {
+      this.schema = schema;
+    }
+
+    public Builder withKeyId(int newKeyId) {
+      this.keyId = newKeyId;
+      return this;
+    }
+
+    public Builder withEnforceUniqueness(boolean enable) {
+      this.enforceUniqueness = enable;
+      return this;
+    }
+
+    public Builder addField(String name) {
+      Types.NestedField column = schema.findField(name);
+
+      Preconditions.checkNotNull(column, "Cannot find source column: %s", name);
+      Preconditions.checkArgument(column.isRequired(), "Cannot add optional source field to primary key: %s", name);
+
+      Type sourceType = column.type();
+      ValidationException.check(sourceType.isPrimitiveType(), "Cannot add non-primitive field: %s", sourceType);
+
+      sourceIds.add(column.fieldId());
+      return this;
+    }
+
+    public Builder addField(int sourceId) {
+      Types.NestedField column = schema.findField(sourceId);
+      Preconditions.checkNotNull(column, "Cannot find source column: %s", sourceId);
+      Preconditions.checkArgument(column.isRequired(), "Cannot add optional source field to primary key: %s", sourceId);

Review comment:
       Other databases (such as MySQL) also do not allow to add `nullable` columns in the primary keys.  see https://dev.mysql.com/doc/refman/8.0/en/create-table.html: 
   
   > A unique index where all key columns must be defined as NOT NULL. If they are not explicitly declared as NOT NULL, MySQL declares them so implicitly (and silently). A table can have only one PRIMARY KEY. The name of a PRIMARY KEY is always PRIMARY, which thus cannot be used as the name for any other kind of index. 




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