DynamoDBMapper-Abfrage und -Scanoperationen

Das Java-Beispiel in diesem Abschnitt definiert die folgenden Klassen und weist sie den Tabellen in Amazon DynamoDB zu. Weitere Informationen zum Erstellen von Beispieltabellen finden Sie unter Erstellen von Tabellen und Laden von Daten für Codebeispiele in DynamoDB.

• Die Klasse Book ist der Tabelle ProductCatalog zugewiesen.

• Die Klassen Forum, Thread und Reply sind Tabellen des gleichen Namens zugeordnet.

Das Beispiel führt anschließend die folgenden Abfrage- und Scan-Operationen mithilfe einer DynamoDBMapper-Instance aus.

• Rufen Sie Bücher nach Id ab.

  Die Tabelle ProductCatalog verwendet Id als Primärschlüssel. Sie verfügt über keinen Sortierschlüssel als Teil ihres Primärschlüssels. Daher können Sie die Tabelle nicht abfragen. Sie können ein Element abrufen, indem Sie dessen Id-Wert verwenden.

• Führen Sie die folgenden Abfragen für die Reply-Tabelle durch.

  Der Primärschlüssel der Tabelle Reply besteht aus den Attributen Id und ReplyDateTime. ReplyDateTime ist ein Sortierschlüssel. Daher können Sie diese Tabelle abfragen.

  • Finden Sie Antworten zu einem Forum-Thread, die in den letzten 15 Tagen gepostet wurden.

  • Finden Sie Antworten zu einem Forum-Thread aus einem bestimmten Zeitraum.

• Scannen Sie die Tabelle ProductCatalog, um Bücher zu finden, deren Preis unter einem angegebenen Wert liegt.

  Aus Leistungsgründen sollten Sie eine Abfrageoperation und keine Scan-Operation verwenden. Manchmal müssen Sie jedoch möglicherweise eine Tabelle scannen. Angenommen, es gab einen Dateneingabefehler und ein Buchpreis wurde auf kleiner als 0 festgelegt. Dieses Beispiel scannt die Tabelle ProductCategory, um Buchelemente zu finden (ProductCategory ist Buch), deren Preis kleiner als 0 ist.

• Führen Sie eine parallelen Scan der Tabelle ProductCatalog aus, um Fahrräder eines bestimmten Typs zu finden.

Anmerkung

In diesem Codebeispiel wird davon ausgegangen, dass Sie bereits Daten für Ihr Konto in DynamoDB geladen haben, indem Sie die Anweisungen im Abschnitt Erstellen von Tabellen und Laden von Daten für Codebeispiele in DynamoDB befolgen.

step-by-step Anweisungen zum Ausführen des folgenden Beispiels finden Sie unter Java-Codebeispiele.

Importe

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;

Code

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;
        }
    }
}