geode-docs/developing/data_serialization/use_pdx_serializable.html.md.erb

---
title:  Implementing PdxSerializable in Your Domain Object
---

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For a domain object with source that you can modify, implement the `PdxSerializable` interface in the object and use its methods to serialize and deserialize the object's fields.

<a id="use_pdx_serializable__section_7F357A8E56B54BFB9A5778C0F89E034E"></a>
**Procedure**

1.  In your domain class, implement `PdxSerializable`, importing the required `org.apache.geode.pdx` classes.

    For example:

    ``` pre
    import org.apache.geode.pdx.PdxReader;
    import org.apache.geode.pdx.PdxSerializable;
    import org.apache.geode.pdx.PdxWriter;

    public class PortfolioPdx implements PdxSerializable {
      ...
    ```

2.  If your domain class does not have a zero-arg constructor, create one for it.

    For example:

    ``` pre
    public PortfolioPdx(){}
    ```

3.  Program `PdxSerializable.toData.`
    1.  Write each standard Java data field of your domain class using the `PdxWriter` write methods. <%=vars.product_name%> automatically provides `PdxWriter` to the `toData` method for `PdxSerializable` objects.
    2.  Call the `PdxWriter` `markIdentifyField` method for each field you want to have <%=vars.product_name%> use to identify your object. Put this after the field's write method. <%=vars.product_name%> uses this information to compare objects for operations like distinct queries. If you do not set as least one identity field, then the `equals` and `hashCode` methods will use all PDX fields to compare objects and consequently, will not perform as well. It is important that the fields used by your `equals` and `hashCode` implementations are the same fields that you mark as identity fields.
    3.  For a particular version of your class, you need to consistently write the same named field each time. The field names or number of fields must not change from one instance to another for the same class version.
    4.  For best performance, do fixed width fields first and then variable length fields.

        Example `toData` code:

        ``` pre
        // PortfolioPdx fields
          private int id;
          private String pkid;
          private Map<String, PositionPdx> positions;
          private String type;
          private String status;
          private String[] names;
          private byte[] newVal;
          private Date creationDate;
          ...

          public void toData(PdxWriter writer)
          {
            writer.writeInt("id", id)
        // The markIdentifyField call for a field must 
        // come after the field's write method 
            .markIdentityField("id")
            .writeDate("creationDate", creationDate) //fixed length field
            .writeString("pkid", pkid)
            .writeObject("positions", positions)
            .writeString("type", type)
            .writeString("status", status)
            .writeStringArray("names", names)
            .writeByteArray("newVal", newVal)
          }
        ```

4.  Program `PdxSerializable.fromData` to read your data fields from the serialized form into the object's fields using the `PdxReader` read methods.

    Provide the same names that you did in `toData` and call the read operations in the same order as you called the write operations in your `toData` implementation.

    <%=vars.product_name%> automatically provides `PdxReader` to the `fromData` method for `PdxSerializable` objects.

    Example `fromData` code:

    ``` pre
      
    public void fromData(PdxReader reader)
      {
        id = reader.readInt("id");
        creationDate = reader.readDate("creationDate");
        pkid = reader.readString("pkid");
        position1 = (PositionPdx)reader.readObject("position1");
        position2 = (PositionPdx)reader.readObject("position2");
        positions = (Map<String, PositionPdx>)reader.readObject("positions");
        type = reader.readString("type");
        status = reader.readString("status");
        names = reader.readStringArray("names");
        newVal = reader.readByteArray("newVal");
        arrayNull = reader.readByteArray("arrayNull");
        arrayZeroSize = reader.readByteArray("arrayZeroSize");
      }
    ```

**What to do next**

-   As needed, configure and program your <%=vars.product_name%> applications to use `PdxInstance` for selective object deserialization. See [Programming Your Application to Use PdxInstances](program_application_for_pdx.html).