Apache Geode Native C++

Using the PdxSerializable Abstract Class

When you write objects using PDX serialization, they are distributed to the server tier in PDX serialized form. Domain classes need to inherit the PdxSerializable abstract class to serialize and de-serialize the object.

When you run queries against the objects on the servers, only the fields you specify are deserialized. A domain class should serialize and de-serialize all its member fields in the same order in its toData and fromData functions.

Use this procedure to program your domain object for PDX serialization using the PdxSerializable abstract class.

1. In your domain class, implement PdxSerializable. For example:

   class Order : public PdxSerializable {
   

2. Program the toData function to serialize your object as required by your application. (See markIdentityField in a later step for an optimization that you can apply to this code sample.)

   void Order::toData(PdxWriter& pdxWriter) const {
     pdxWriter.writeInt(ORDER_ID_KEY_, order_id_);
     pdxWriter.writeString(NAME_KEY_, name_);
     pdxWriter.writeShort(QUANTITY_KEY_, quantity_);
   }
   

   If you also use PDX serialization in Java or .NET for the object, serialize the object in the same way for each language. Serialize the same fields in the same order and mark the same identity fields.

3. Program the fromData function to read your data fields from the serialized form into the object’s fields.

   void Order::fromData(PdxReader& pdxReader) {
     order_id_ = pdxReader.readInt(ORDER_ID_KEY_);
     name_ = pdxReader.readString(NAME_KEY_);
     quantity_ = pdxReader.readShort(QUANTITY_KEY_);
   }
   

   In your fromData implementation, use the same name as you did in toData and call the read operations in the same order as you called the write operations in your toData implementation.

4. Optionally, program your domain object’s hashCode and equality functions. When you do so, you can optimize those functions by specifying the identity fields to be used in comparisons.
   

   • Marked identity fields are used to generate the hashCode and equality functions of PdxInstance, so the identity fields should themselves either be primitives, or implement hashCode and equals.
     
   • The markIdentityField function indicates that the given field name should be included in hashCode and equality checks of this object on a server.
     
   • Invoke the markIdentityField function directly after the identity field’s write* function.
     
   • If no fields are set as identity fields, then all fields will be used in hashCode and equality checks, so marking identity fields improves the efficiency of hashing and equality operations.
     
   • It is important that the fields used by your equality function and hashCode implementations are the same fields that you mark as identity fields.

   This code sample expands the sample from the description of the toData function, above, to illustrate the use of markIdentityField:

   void Order::toData(PdxWriter& pdxWriter) const {
     pdxWriter.writeInt(ORDER_ID_KEY_, order_id_);
     pdxWriter.markIdentityField(ORDER_ID_KEY_);
   
     pdxWriter.writeString(NAME_KEY_, name_);
     pdxWriter.markIdentityField(NAME_KEY_);
   
     pdxWriter.writeShort(QUANTITY_KEY_, quantity_);
     pdxWriter.markIdentityField(QUANTITY_KEY_);
   }