Bekerja dengan atribut bersarang - AWS SDK for Java 2.x
Petakan atribut bersarangAtribut bersarang proyek

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Bekerja dengan atribut bersarang

Sebuah atribut bersarang di DynamoDB disematkan dalam atribut lain. Contohnya adalah elemen daftar dan entri peta.

Di Java, atribut bersarang DynamoDB sesuai dengan anggota kelas yang merupakan or. List Map Ini juga sesuai dengan contoh dari jenis kompleks, seperti Address atauPhoneNumber, seperti yang digunakan dalam Person kelas berikut.

@DynamoDbBean
public class Person {
    Integer id;
    String firstName;
    String lastName;
    Integer age;
    Map<String, Address> addresses;
    List<PhoneNumber> phoneNumbers;

    List<String> hobbies;

    @DynamoDbPartitionKey
    public Integer getId() {
        return id;
    }

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

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Map<String, Address> getAddresses() {
        return addresses;
    }

    public void setAddresses(Map<String, Address> addresses) {
        this.addresses = addresses;
    }

    public List<PhoneNumber> getPhoneNumbers() {
        return phoneNumbers;
    }

    public void setPhoneNumbers(List<PhoneNumber> phoneNumbers) {
        this.phoneNumbers = phoneNumbers;
    }

    public List<String> getHobbies() {
        return hobbies;
    }

    public void setHobbies(List<String> hobbies) {
        this.hobbies = hobbies;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                ", age=" + age +
                ", addresses=" + addresses +
                ", phoneNumbers=" + phoneNumbers +
                ", hobbies=" + hobbies +
                '}';
    }
}
@DynamoDbBean
public class Address {
    private String street;
    private String city;
    private String state;
    private String zipCode;

    public Address() {
    }

    public String getStreet() {
        return this.street;
    }

    public String getCity() {
        return this.city;
    }

    public String getState() {
        return this.state;
    }

    public String getZipCode() {
        return this.zipCode;
    }

    public void setStreet(String street) {
        this.street = street;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public void setState(String state) {
        this.state = state;
    }

    public void setZipCode(String zipCode) {
        this.zipCode = zipCode;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Address address = (Address) o;
        return Objects.equals(street, address.street) && Objects.equals(city, address.city) && Objects.equals(state, address.state) && Objects.equals(zipCode, address.zipCode);
    }

    @Override
    public int hashCode() {
        return Objects.hash(street, city, state, zipCode);
    }

    @Override
    public String toString() {
        return "Address{" +
                "street='" + street + '\'' +
                ", city='" + city + '\'' +
                ", state='" + state + '\'' +
                ", zipCode='" + zipCode + '\'' +
                '}';
    }
}
@DynamoDbBean
public class PhoneNumber {
    String type;
    String number;

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    @Override
    public String toString() {
        return "PhoneNumber{" +
                "type='" + type + '\'' +
                ", number='" + number + '\'' +
                '}';
    }
}

Petakan atribut bersarang

Gunakan kelas beranotasi

Anda dapat menyimpan atribut bersarang untuk kelas kustom dengan membuat anotasi. AddressKelas dan PhoneNumber kelas yang ditampilkan sebelumnya dianotasi hanya dengan anotasi. @DynamoDbBean Saat DynamoDB Enhanced Client API membangun skema tabel untuk Person kelas dengan cuplikan berikut, API akan menemukan penggunaan class PhoneNumber dan dan membangun pemetaan yang sesuai agar berfungsi dengan DynamoDB. Address

TableSchema<Person> personTableSchema = TableSchema.fromBean(Person.class);

Gunakan skema bersarang

Pendekatan alternatif adalah dengan menggunakan pembangun skema tabel statis untuk masing-masing kelas seperti yang ditunjukkan dalam kode berikut.

Skema tabel untuk PhoneNumber kelas Address dan abstrak dalam arti bahwa mereka tidak dapat digunakan dengan tabel DynamoDB. Ini karena mereka tidak memiliki definisi untuk kunci utama. Mereka digunakan, bagaimanapun, sebagai skema bersarang dalam skema tabel untuk kelas. Person

Setelah baris komentar 1 dan 2 dalam definisiPERSON_TABLE_SCHEMA, Anda melihat kode yang menggunakan skema tabel abstrak. Penggunaan documentOf dalam EnhanceType.documentOf(...) metode ini tidak menunjukkan bahwa metode mengembalikan EnhancedDocument jenis API Dokumen yang Ditingkatkan. documentOf(...)Metode dalam konteks ini mengembalikan objek yang tahu bagaimana memetakan argumen kelasnya ke dan dari DynamoDB atribut tabel dengan menggunakan argumen skema tabel.

    // Abstract table schema that cannot be used to work with a DynamoDB table,
    // but can be used as a nested schema.
    public static final TableSchema<Address> TABLE_SCHEMA_ADDRESS = TableSchema.builder(Address.class)
            .newItemSupplier(Address::new)
            .addAttribute(String.class, a -> a.name("street")
                    .getter(Address::getStreet)
                    .setter(Address::setStreet))
            .addAttribute(String.class, a -> a.name("city")
                    .getter(Address::getCity)
                    .setter(Address::setCity))
            .addAttribute(String.class, a -> a.name("zipcode")
                    .getter(Address::getZipCode)
                    .setter(Address::setZipCode))
            .addAttribute(String.class, a -> a.name("state")
                    .getter(Address::getState)
                    .setter(Address::setState))
            .build();

    // Abstract table schema that cannot be used to work with a DynamoDB table,
    // but can be used as a nested schema.
    public static final TableSchema<PhoneNumber> TABLE_SCHEMA_PHONENUMBER = TableSchema.builder(PhoneNumber.class)
            .newItemSupplier(PhoneNumber::new)
            .addAttribute(String.class, a -> a.name("type")
                    .getter(PhoneNumber::getType)
                    .setter(PhoneNumber::setType))
            .addAttribute(String.class, a -> a.name("number")
                    .getter(PhoneNumber::getNumber)
                    .setter(PhoneNumber::setNumber))
            .build();

    // A static table schema that can be used with a DynamoDB table.
    // The table schema contains two nested schemas that are used to perform mapping to/from DynamoDB.
    public static final TableSchema<Person> PERSON_TABLE_SCHEMA =
            TableSchema.builder(Person.class)
                    .newItemSupplier(Person::new)
                    .addAttribute(Integer.class, a -> a.name("id")
                            .getter(Person::getId)
                            .setter(Person::setId)
                            .addTag(StaticAttributeTags.primaryPartitionKey()))
                    .addAttribute(String.class, a -> a.name("firstName")
                            .getter(Person::getFirstName)
                            .setter(Person::setFirstName))
                    .addAttribute(String.class, a -> a.name("lastName")
                            .getter(Person::getLastName)
                            .setter(Person::setLastName))
                    .addAttribute(Integer.class, a -> a.name("age")
                            .getter(Person::getAge)
                            .setter(Person::setAge))
                    .addAttribute(EnhancedType.listOf(String.class), a -> a.name("hobbies")
                            .getter(Person::getHobbies)
                            .setter(Person::setHobbies))
                    .addAttribute(EnhancedType.mapOf(
                            EnhancedType.of(String.class),
                            // 1. Use mapping functionality of the Address table schema.
                            EnhancedType.documentOf(Address.class, TABLE_SCHEMA_ADDRESS)), a -> a.name("addresses")
                            .getter(Person::getAddresses)
                            .setter(Person::setAddresses))
                    .addAttribute(EnhancedType.listOf(
                            // 2. Use mapping functionality of the PhoneNumber table schema.
                            EnhancedType.documentOf(PhoneNumber.class, TABLE_SCHEMA_PHONENUMBER)), a -> a.name("phoneNumbers")
                            .getter(Person::getPhoneNumbers)
                            .setter(Person::setPhoneNumbers))
                    .build();

Atribut bersarang proyek

Untuk query() dan scan() metode, Anda dapat menentukan atribut mana yang ingin Anda kembalikan dalam hasil dengan menggunakan panggilan metode seperti addNestedAttributeToProject() danattributesToProject(). DynamoDB Enhanced Client API mengubah parameter panggilan metode Java menjadi ekspresi proyeksi sebelum permintaan dikirim.

Contoh berikut mengisi Person tabel dengan dua item, kemudian melakukan tiga operasi pemindaian.

Pemindaian pertama mengakses semua item dalam tabel untuk membandingkan hasilnya dengan operasi pemindaian lainnya.

Pemindaian kedua menggunakan metode addNestedAttributeToProject()builder untuk mengembalikan hanya nilai street atribut.

Operasi pemindaian ketiga menggunakan metode attributesToProject()builder untuk mengembalikan data untuk atribut tingkat pertama,hobbies. Jenis atribut hobbies adalah daftar. Untuk mengakses item daftar individual, lakukan get() operasi pada daftar.

        personDynamoDbTable = getDynamoDbEnhancedClient().table("Person", PERSON_TABLE_SCHEMA);
        PersonUtils.createPersonTable(personDynamoDbTable, getDynamoDbClient());
        // Use a utility class to add items to the Person table.
        List<Person> personList = PersonUtils.getItemsForCount(2);
        // This utility method performs a put against DynamoDB to save the instances in the list argument.
        PersonUtils.putCollection(getDynamoDbEnhancedClient(), personList, personDynamoDbTable);

        // The first scan logs all items in the table to compare to the results of the subsequent scans.
        final PageIterable<Person> allItems = personDynamoDbTable.scan();
        allItems.items().forEach(p ->
                // 1. Log what is in the table.
                logger.info(p.toString()));

        // Scan for nested attributes.
        PageIterable<Person> streetScanResult = personDynamoDbTable.scan(b -> b
                // Use the 'addNestedAttributeToProject()' or 'addNestedAttributesToProject()' to access data nested in maps in DynamoDB.
                .addNestedAttributeToProject(
                        NestedAttributeName.create("addresses", "work", "street")
                ));

        streetScanResult.items().forEach(p ->
                //2. Log the results of requesting nested attributes.
                logger.info(p.toString()));

        // Scan for a top-level list attribute.
        PageIterable<Person> phoneNumbersScanResult = personDynamoDbTable.scan(b -> b
                // Use the 'attributesToProject()' method to access first-level attributes.
                .attributesToProject("hobbies"));

        phoneNumbersScanResult.items().forEach((p) -> {
            // 3. Log the results of the request for the 'hobbies' attribute.
            logger.info(p.toString());
            // To access an item in a list, first get the parent attribute, 'hobbies', then access items in the list.
            String hobby = p.getHobbies().get(1);
            // 4. Log an item in the list.
            logger.info(hobby);
        });

// Logged results from comment line 1.
Person{id=2, firstName='first name 2', lastName='last name 2', age=11, addresses={work=Address{street='street 21', city='city 21', state='state 21', zipCode='33333'}, home=Address{street='street 2', city='city 2', state='state 2', zipCode='22222'}}, phoneNumbers=[PhoneNumber{type='home', number='222-222-2222'}, PhoneNumber{type='work', number='333-333-3333'}], hobbies=[hobby 2, hobby 21]}
Person{id=1, firstName='first name 1', lastName='last name 1', age=11, addresses={work=Address{street='street 11', city='city 11', state='state 11', zipCode='22222'}, home=Address{street='street 1', city='city 1', state='state 1', zipCode='11111'}}, phoneNumbers=[PhoneNumber{type='home', number='111-111-1111'}, PhoneNumber{type='work', number='222-222-2222'}], hobbies=[hobby 1, hobby 11]}

// Logged results from comment line 2.
Person{id=null, firstName='null', lastName='null', age=null, addresses={work=Address{street='street 21', city='null', state='null', zipCode='null'}}, phoneNumbers=null, hobbies=null}
Person{id=null, firstName='null', lastName='null', age=null, addresses={work=Address{street='street 11', city='null', state='null', zipCode='null'}}, phoneNumbers=null, hobbies=null}

// Logged results from comment lines 3 and 4.
Person{id=null, firstName='null', lastName='null', age=null, addresses=null, phoneNumbers=null, hobbies=[hobby 2, hobby 21]}
hobby 21
Person{id=null, firstName='null', lastName='null', age=null, addresses=null, phoneNumbers=null, hobbies=[hobby 1, hobby 11]}
hobby 11
catatan

Jika attributesToProject() metode mengikuti metode pembangun lain yang menambahkan atribut yang ingin Anda proyeksikan, daftar nama atribut yang diberikan ke attributesToProject() menggantikan semua nama atribut lainnya.

Pemindaian yang dilakukan dengan ScanEnhancedRequest instance dalam cuplikan berikut hanya mengembalikan data hobi.

ScanEnhancedRequest lastOverwrites = ScanEnhancedRequest.builder()
        .addNestedAttributeToProject(
                NestedAttributeName.create("addresses", "work", "street"))
        .addAttributeToProject("firstName")
        // If the 'attributesToProject()' method follows other builder methods that add attributes for projection,
        // its list of attributes replace all previous attributes.
        .attributesToProject("hobbies")
        .build();
PageIterable<Person> hobbiesOnlyResult = personDynamoDbTable.scan(lastOverwrites);
hobbiesOnlyResult.items().forEach(p ->
        logger.info(p.toString()));

// Logged results.
Person{id=null, firstName='null', lastName='null', age=null, addresses=null, phoneNumbers=null, hobbies=[hobby 2, hobby 21]}
Person{id=null, firstName='null', lastName='null', age=null, addresses=null, phoneNumbers=null, hobbies=[hobby 1, hobby 11]}

Cuplikan kode berikut menggunakan attributesToProject() metode terlebih dahulu. Urutan ini mempertahankan semua atribut lain yang diminta.

ScanEnhancedRequest attributesPreserved = ScanEnhancedRequest.builder()
        // Use 'attributesToProject()' first so that the method call does not replace all other attributes
        // that you want to project.
        .attributesToProject("firstName")
        .addNestedAttributeToProject(
                NestedAttributeName.create("addresses", "work", "street"))
        .addAttributeToProject("hobbies")
        .build();
PageIterable<Person> allAttributesResult = personDynamoDbTable.scan(attributesPreserved);
allAttributesResult.items().forEach(p ->
        logger.info(p.toString()));

// Logged results.
Person{id=null, firstName='first name 2', lastName='null', age=null, addresses={work=Address{street='street 21', city='null', state='null', zipCode='null'}}, phoneNumbers=null, hobbies=[hobby 2, hobby 21]}
Person{id=null, firstName='first name 1', lastName='null', age=null, addresses={work=Address{street='street 11', city='null', state='null', zipCode='null'}}, phoneNumbers=null, hobbies=[hobby 1, hobby 11]}