Operações de consulta e varredura com DynamoDBMapper

O exemplo de Java nesta seção define as seguintes classes e as mapeia nas tabelas do Amazon DynamoDB. Para obter mais informações sobre como criar tabelas de exemplo, consulte Criar tabelas e carregar dados para exemplos de código no DynamoDB.

• A classe Book mapeia para a tabela ProductCatalog

• As classes Forum, Thread e Reply são mapeadas nas tabelas de mesmo nome.

O exemplo executa as seguintes operações de consulta e verificação usando uma instância de DynamoDBMapper.

• Obtenha um livro por Id.

  A tabela ProductCatalog tem Id como sua chave primária. Ela não tem uma chave de classificação como parte de sua chave primária. Portanto, você não pode consultar a tabela. É possível obter um item usando o valor Id.

• Execute as consultas a seguir na tabela Reply.

  A chave primária da tabela Reply composta por atributos Id e ReplyDateTime. ReplyDateTime é uma chave de classificação. Portanto, é possível consultar essa tabela.

  • Localize respostas para um tópico de fórum postado nos últimos 15 dias.

  • Localize respostas para um tópico de fórum postado em um intervalo de datas específico.

• Verifique a tabela ProductCatalog para localizar livros cujo preço seja menor que um valor especificado.

  Por motivos de desempenho, é necessário usar uma operação de consulta, em vez de uma operação de verificação. No entanto, em algumas ocasiões, talvez você precise verificar uma tabela. Vamos supor que tenha ocorrido um erro de entrada de dados e que um dos preços de livros tenha sido definido como menor que 0. Este exemplo verifica a tabela ProductCategory para localizar itens de livro (ProductCategory é livro) cujos preços são menores que 0.

• Realize uma verificação paralela da tabela ProductCatalog para localizar bicicletas de um tipo específico.

nota

Este exemplo de código pressupõe que você já carregou dados no DynamoDB para sua conta seguindo as instruções na seção Criar tabelas e carregar dados para exemplos de código no DynamoDB.

Para step-by-step obter instruções sobre como executar o exemplo a seguir, consulteExemplos de código Java.

Importações

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TimeZone;

import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBAttribute;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBHashKey;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBQueryExpression;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBRangeKey;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBScanExpression;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTable;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;

Código

public class DynamoDBMapperQueryScanExample {

    static AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();

    public static void main(String[] args) throws Exception {
        try {

            DynamoDBMapper mapper = new DynamoDBMapper(client);

            // Get a book - Id=101
            GetBook(mapper, 101);
            // Sample forum and thread to test queries.
            String forumName = "Amazon DynamoDB";
            String threadSubject = "DynamoDB Thread 1";
            // Sample queries.
            FindRepliesInLast15Days(mapper, forumName, threadSubject);
            FindRepliesPostedWithinTimePeriod(mapper, forumName, threadSubject);

            // Scan a table and find book items priced less than specified
            // value.
            FindBooksPricedLessThanSpecifiedValue(mapper, "20");

            // Scan a table with multiple threads and find bicycle items with a
            // specified bicycle type
            int numberOfThreads = 16;
            FindBicyclesOfSpecificTypeWithMultipleThreads(mapper, numberOfThreads, "Road");

            System.out.println("Example complete!");

        } catch (Throwable t) {
            System.err.println("Error running the DynamoDBMapperQueryScanExample: " + t);
            t.printStackTrace();
        }
    }

    private static void GetBook(DynamoDBMapper mapper, int id) throws Exception {
        System.out.println("GetBook: Get book Id='101' ");
        System.out.println("Book table has no sort key. You can do GetItem, but not Query.");
        Book book = mapper.load(Book.class, id);
        System.out.format("Id = %s Title = %s, ISBN = %s %n", book.getId(), book.getTitle(), book.getISBN());
    }

    private static void FindRepliesInLast15Days(DynamoDBMapper mapper, String forumName, String threadSubject)
            throws Exception {
        System.out.println("FindRepliesInLast15Days: Replies within last 15 days.");

        String partitionKey = forumName + "#" + threadSubject;

        long twoWeeksAgoMilli = (new Date()).getTime() - (15L * 24L * 60L * 60L * 1000L);
        Date twoWeeksAgo = new Date();
        twoWeeksAgo.setTime(twoWeeksAgoMilli);
        SimpleDateFormat dateFormatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");
        dateFormatter.setTimeZone(TimeZone.getTimeZone("UTC"));
        String twoWeeksAgoStr = dateFormatter.format(twoWeeksAgo);

        Map<String, AttributeValue> eav = new HashMap<String, AttributeValue>();
        eav.put(":val1", new AttributeValue().withS(partitionKey));
        eav.put(":val2", new AttributeValue().withS(twoWeeksAgoStr.toString()));

        DynamoDBQueryExpression<Reply> queryExpression = new DynamoDBQueryExpression<Reply>()
                .withKeyConditionExpression("Id = :val1 and ReplyDateTime > :val2").withExpressionAttributeValues(eav);

        List<Reply> latestReplies = mapper.query(Reply.class, queryExpression);

        for (Reply reply : latestReplies) {
            System.out.format("Id=%s, Message=%s, PostedBy=%s %n, ReplyDateTime=%s %n", reply.getId(),
                    reply.getMessage(), reply.getPostedBy(), reply.getReplyDateTime());
        }
    }

    private static void FindRepliesPostedWithinTimePeriod(DynamoDBMapper mapper, String forumName, String threadSubject)
            throws Exception {
        String partitionKey = forumName + "#" + threadSubject;

        System.out.println(
                "FindRepliesPostedWithinTimePeriod: Find replies for thread Message = 'DynamoDB Thread 2' posted within a period.");
        long startDateMilli = (new Date()).getTime() - (14L * 24L * 60L * 60L * 1000L); // Two
                                                                                        // weeks
                                                                                        // ago.
        long endDateMilli = (new Date()).getTime() - (7L * 24L * 60L * 60L * 1000L); // One
                                                                                     // week
                                                                                     // ago.
        SimpleDateFormat dateFormatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");
        dateFormatter.setTimeZone(TimeZone.getTimeZone("UTC"));
        String startDate = dateFormatter.format(startDateMilli);
        String endDate = dateFormatter.format(endDateMilli);

        Map<String, AttributeValue> eav = new HashMap<String, AttributeValue>();
        eav.put(":val1", new AttributeValue().withS(partitionKey));
        eav.put(":val2", new AttributeValue().withS(startDate));
        eav.put(":val3", new AttributeValue().withS(endDate));

        DynamoDBQueryExpression<Reply> queryExpression = new DynamoDBQueryExpression<Reply>()
                .withKeyConditionExpression("Id = :val1 and ReplyDateTime between :val2 and :val3")
                .withExpressionAttributeValues(eav);

        List<Reply> betweenReplies = mapper.query(Reply.class, queryExpression);

        for (Reply reply : betweenReplies) {
            System.out.format("Id=%s, Message=%s, PostedBy=%s %n, PostedDateTime=%s %n", reply.getId(),
                    reply.getMessage(), reply.getPostedBy(), reply.getReplyDateTime());
        }

    }

    private static void FindBooksPricedLessThanSpecifiedValue(DynamoDBMapper mapper, String value) throws Exception {

        System.out.println("FindBooksPricedLessThanSpecifiedValue: Scan ProductCatalog.");

        Map<String, AttributeValue> eav = new HashMap<String, AttributeValue>();
        eav.put(":val1", new AttributeValue().withN(value));
        eav.put(":val2", new AttributeValue().withS("Book"));

        DynamoDBScanExpression scanExpression = new DynamoDBScanExpression()
                .withFilterExpression("Price < :val1 and ProductCategory = :val2").withExpressionAttributeValues(eav);

        List<Book> scanResult = mapper.scan(Book.class, scanExpression);

        for (Book book : scanResult) {
            System.out.println(book);
        }
    }

    private static void FindBicyclesOfSpecificTypeWithMultipleThreads(DynamoDBMapper mapper, int numberOfThreads,
            String bicycleType) throws Exception {

        System.out.println("FindBicyclesOfSpecificTypeWithMultipleThreads: Scan ProductCatalog With Multiple Threads.");
        Map<String, AttributeValue> eav = new HashMap<String, AttributeValue>();
        eav.put(":val1", new AttributeValue().withS("Bicycle"));
        eav.put(":val2", new AttributeValue().withS(bicycleType));

        DynamoDBScanExpression scanExpression = new DynamoDBScanExpression()
                .withFilterExpression("ProductCategory = :val1 and BicycleType = :val2")
                .withExpressionAttributeValues(eav);

        List<Bicycle> scanResult = mapper.parallelScan(Bicycle.class, scanExpression, numberOfThreads);
        for (Bicycle bicycle : scanResult) {
            System.out.println(bicycle);
        }
    }

    @DynamoDBTable(tableName = "ProductCatalog")
    public static class Book {
        private int id;
        private String title;
        private String ISBN;
        private int price;
        private int pageCount;
        private String productCategory;
        private boolean inPublication;

        @DynamoDBHashKey(attributeName = "Id")
        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        @DynamoDBAttribute(attributeName = "Title")
        public String getTitle() {
            return title;
        }

        public void setTitle(String title) {
            this.title = title;
        }

        @DynamoDBAttribute(attributeName = "ISBN")
        public String getISBN() {
            return ISBN;
        }

        public void setISBN(String ISBN) {
            this.ISBN = ISBN;
        }

        @DynamoDBAttribute(attributeName = "Price")
        public int getPrice() {
            return price;
        }

        public void setPrice(int price) {
            this.price = price;
        }

        @DynamoDBAttribute(attributeName = "PageCount")
        public int getPageCount() {
            return pageCount;
        }

        public void setPageCount(int pageCount) {
            this.pageCount = pageCount;
        }

        @DynamoDBAttribute(attributeName = "ProductCategory")
        public String getProductCategory() {
            return productCategory;
        }

        public void setProductCategory(String productCategory) {
            this.productCategory = productCategory;
        }

        @DynamoDBAttribute(attributeName = "InPublication")
        public boolean getInPublication() {
            return inPublication;
        }

        public void setInPublication(boolean inPublication) {
            this.inPublication = inPublication;
        }

        @Override
        public String toString() {
            return "Book [ISBN=" + ISBN + ", price=" + price + ", product category=" + productCategory + ", id=" + id
                    + ", title=" + title + "]";
        }

    }

    @DynamoDBTable(tableName = "ProductCatalog")
    public static class Bicycle {
        private int id;
        private String title;
        private String description;
        private String bicycleType;
        private String brand;
        private int price;
        private List<String> color;
        private String productCategory;

        @DynamoDBHashKey(attributeName = "Id")
        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        @DynamoDBAttribute(attributeName = "Title")
        public String getTitle() {
            return title;
        }

        public void setTitle(String title) {
            this.title = title;
        }

        @DynamoDBAttribute(attributeName = "Description")
        public String getDescription() {
            return description;
        }

        public void setDescription(String description) {
            this.description = description;
        }

        @DynamoDBAttribute(attributeName = "BicycleType")
        public String getBicycleType() {
            return bicycleType;
        }

        public void setBicycleType(String bicycleType) {
            this.bicycleType = bicycleType;
        }

        @DynamoDBAttribute(attributeName = "Brand")
        public String getBrand() {
            return brand;
        }

        public void setBrand(String brand) {
            this.brand = brand;
        }

        @DynamoDBAttribute(attributeName = "Price")
        public int getPrice() {
            return price;
        }

        public void setPrice(int price) {
            this.price = price;
        }

        @DynamoDBAttribute(attributeName = "Color")
        public List<String> getColor() {
            return color;
        }

        public void setColor(List<String> color) {
            this.color = color;
        }

        @DynamoDBAttribute(attributeName = "ProductCategory")
        public String getProductCategory() {
            return productCategory;
        }

        public void setProductCategory(String productCategory) {
            this.productCategory = productCategory;
        }

        @Override
        public String toString() {
            return "Bicycle [Type=" + bicycleType + ", color=" + color + ", price=" + price + ", product category="
                    + productCategory + ", id=" + id + ", title=" + title + "]";
        }

    }

    @DynamoDBTable(tableName = "Reply")
    public static class Reply {
        private String id;
        private String replyDateTime;
        private String message;
        private String postedBy;

        // Partition key
        @DynamoDBHashKey(attributeName = "Id")
        public String getId() {
            return id;
        }

        public void setId(String id) {
            this.id = id;
        }

        // Range key
        @DynamoDBRangeKey(attributeName = "ReplyDateTime")
        public String getReplyDateTime() {
            return replyDateTime;
        }

        public void setReplyDateTime(String replyDateTime) {
            this.replyDateTime = replyDateTime;
        }

        @DynamoDBAttribute(attributeName = "Message")
        public String getMessage() {
            return message;
        }

        public void setMessage(String message) {
            this.message = message;
        }

        @DynamoDBAttribute(attributeName = "PostedBy")
        public String getPostedBy() {
            return postedBy;
        }

        public void setPostedBy(String postedBy) {
            this.postedBy = postedBy;
        }
    }

    @DynamoDBTable(tableName = "Thread")
    public static class Thread {
        private String forumName;
        private String subject;
        private String message;
        private String lastPostedDateTime;
        private String lastPostedBy;
        private Set<String> tags;
        private int answered;
        private int views;
        private int replies;

        // Partition key
        @DynamoDBHashKey(attributeName = "ForumName")
        public String getForumName() {
            return forumName;
        }

        public void setForumName(String forumName) {
            this.forumName = forumName;
        }

        // Range key
        @DynamoDBRangeKey(attributeName = "Subject")
        public String getSubject() {
            return subject;
        }

        public void setSubject(String subject) {
            this.subject = subject;
        }

        @DynamoDBAttribute(attributeName = "Message")
        public String getMessage() {
            return message;
        }

        public void setMessage(String message) {
            this.message = message;
        }

        @DynamoDBAttribute(attributeName = "LastPostedDateTime")
        public String getLastPostedDateTime() {
            return lastPostedDateTime;
        }

        public void setLastPostedDateTime(String lastPostedDateTime) {
            this.lastPostedDateTime = lastPostedDateTime;
        }

        @DynamoDBAttribute(attributeName = "LastPostedBy")
        public String getLastPostedBy() {
            return lastPostedBy;
        }

        public void setLastPostedBy(String lastPostedBy) {
            this.lastPostedBy = lastPostedBy;
        }

        @DynamoDBAttribute(attributeName = "Tags")
        public Set<String> getTags() {
            return tags;
        }

        public void setTags(Set<String> tags) {
            this.tags = tags;
        }

        @DynamoDBAttribute(attributeName = "Answered")
        public int getAnswered() {
            return answered;
        }

        public void setAnswered(int answered) {
            this.answered = answered;
        }

        @DynamoDBAttribute(attributeName = "Views")
        public int getViews() {
            return views;
        }

        public void setViews(int views) {
            this.views = views;
        }

        @DynamoDBAttribute(attributeName = "Replies")
        public int getReplies() {
            return replies;
        }

        public void setReplies(int replies) {
            this.replies = replies;
        }

    }

    @DynamoDBTable(tableName = "Forum")
    public static class Forum {
        private String name;
        private String category;
        private int threads;

        @DynamoDBHashKey(attributeName = "Name")
        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        @DynamoDBAttribute(attributeName = "Category")
        public String getCategory() {
            return category;
        }

        public void setCategory(String category) {
            this.category = category;
        }

        @DynamoDBAttribute(attributeName = "Threads")
        public int getThreads() {
            return threads;
        }

        public void setThreads(int threads) {
            this.threads = threads;
        }
    }
}