@Entity
@Data
public class Purchase {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private Integer count;
    private String name;
    private String lastName;
    private Integer age;
    private BigDecimal amount;
    private LocalDateTime purchaseDate;
    @ManyToOne
    private Item purchaseItem;
}

<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="Purchase" >
        <xs:complexType>
            <xs:sequence>
                <xs:element type="xs:long" name="id"/>
                <xs:element type="xs:integer" name="count"  />
                <xs:element type="xs:string" name="name"/>
                <xs:element type="xs:string" name="lastName"/>
                <xs:element type="xs:integer" name="age"/>
                <xs:element type="xs:decimal" name="amount"/>
                <xs:element type="xs:dateTime" name="purchaseDate"/>
                <xs:element name="purchaseItem">
                    <xs:complexType>
                        <xs:sequence>
                            <xs:element type="xs:long" name="id"/>
                            <xs:element type="xs:string" name="name"/>
                        </xs:sequence>
                    </xs:complexType>
                </xs:element>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>