使用不可變的資料類別

DynamoDB 增強型用戶端 API 的對應功能可與不可變的資料類別搭配使用。不可變類只有 getter，並且需要 SDK 用於創建類實例的構建器類。不可變類別不會使用 Custo mer 類別中所示的@DynamoDbBean註解，而是使用@DynamoDbImmutable註解，註解會接受指示要使用的建構器類別的參數。

下列類別是的不可變版本Customer。

package org.example.tests.model.immutable;

import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbImmutable;
import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbPartitionKey;
import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbSecondaryPartitionKey;
import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbSecondarySortKey;
import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbSortKey;

import java.time.Instant;

@DynamoDbImmutable(builder = CustomerImmutable.Builder.class)
public class CustomerImmutable {
    private final String id;
    private final String name;
    private final String email;
    private final Instant regDate;

    private CustomerImmutable(Builder b) {
        this.id = b.id;
        this.email = b.email;
        this.name = b.name;
        this.regDate = b.regDate;
    }

    // This method will be automatically discovered and used by the TableSchema.
    public static Builder builder() { return new Builder(); }

    @DynamoDbPartitionKey
    public String id() { return this.id; }

    @DynamoDbSortKey
    public String email() { return this.email; }

    @DynamoDbSecondaryPartitionKey(indexNames = "customers_by_name")
    public String name() { return this.name; }

    @DynamoDbSecondarySortKey(indexNames = {"customers_by_date", "customers_by_name"})
    public Instant regDate() { return this.regDate; }

    public static final class Builder {
        private String id;
        private String email;
        private String name;
        private Instant regDate;

        // The private Builder constructor is visible to the enclosing CustomerImmutable class.
        private Builder() {}

        public Builder id(String id) { this.id = id; return this; }
        public Builder email(String email) { this.email = email; return this; }
        public Builder name(String name) { this.name = name; return this; }
        public Builder regDate(Instant regDate) { this.regDate = regDate; return this; }

        // This method will be automatically discovered and used by the TableSchema.
        public CustomerImmutable build() { return new CustomerImmutable(this); }
    }
}

當您使用註解資料類別時，您必須符合下列需求@DynamoDbImmutable。

1. 每個不是覆寫Object.class且未被註解的方法，都@DynamoDbIgnore必須是 DynamoDB 表格屬性的吸引器。

2. 每個 getter 必須在構建器類上具有相應的區分大小寫的 setter。

3. 只能滿足下列其中一個施工條件。

   • 構建器類必須有一個公共默認構造函數。

   • 資料類別必須有名為的公用靜態方法，builder()該方法不接受任何參數，並傳回建置器類別的實體。這個選項顯示在不可變的Customer類。

4. 建構器類別必須具有名為的公用方法，build()該方法不接受任何參數，並傳回不可變類別的執行個體。

要TableSchema為您的不可變類創建一個，請使用上的fromImmutableClass()方法，TableSchema如下面的代碼片段。

static final TableSchema<CustomerImmutable> customerImmutableTableSchema = 
                         TableSchema.fromImmutableClass(CustomerImmutable.class);

正如您可以從可變類別建立 DynamoDB 資料表一樣，您可以透過一次性呼叫 of 從不可變類別建立一個資料表，如下列程式碼片段createTable()範DynamoDbTable例所示。

static void createTableFromImmutable(DynamoDbEnhancedClient enhancedClient, String tableName, DynamoDbWaiter waiter){
    // First, create an in-memory representation of the table using the 'table()' method of the DynamoDb Enhanced Client.
    // 'table()' accepts a name for the table and a TableSchema instance that you created previously.
    DynamoDbTable<CustomerImmutable> customerDynamoDbTable = enhancedClient
            .table(tableName, TableSchema.fromImmutableClass(CustomerImmutable.class));
        
    // Second, call the 'createTable()' method on the DynamoDbTable instance.
    customerDynamoDbTable.createTable();
    waiter.waitUntilTableExists(b -> b.tableName(tableName));
}

使用第三方庫，例如龍目島

協力廠商程式庫，例如 Project Log，可協助產生與不可變物件相關聯的樣板程式碼。只要資料類別遵循本節中詳述的慣例，DynamoDB 增強型用戶端 API 就可與這些程式庫搭配使用。

下面的例子顯示了龍目島註釋不可變的CustomerImmutable類。請注意，龍目島的onMethod功能如何將以屬性為基礎的 DynamoDB 註釋 (例如@DynamoDbPartitionKey) 複製到產生的程式碼上。

@Value
@Builder
@DynamoDbImmutable(builder = Customer.CustomerBuilder.class)
public class Customer {
    @Getter(onMethod_=@DynamoDbPartitionKey)
    private String id;

    @Getter(onMethod_=@DynamoDbSortKey)
    private String email;

    @Getter(onMethod_=@DynamoDbSecondaryPartitionKey(indexNames = "customers_by_name"))
    private String name;

    @Getter(onMethod_=@DynamoDbSecondarySortKey(indexNames = {"customers_by_date", "customers_by_name"}))
    private Instant createdDate;
}