#347 - @History support with query.asOf(Timestamp) - javadoc update

src/main/java/com/avaje/ebean/config/dbplatform/DatabasePlatform.java

@@ -442,6 +442,13 @@ public class DatabasePlatform {
     return disallowBatchOnCascade;
   }
 
+  /**
+   * Return the 'as of' predicate added for the given table alias.
+   *
+   * @param asOfTableAlias The table alias this predicate is added for
+   * @param asOfSysPeriod  The name of the 'sys_period' column used for effective date time range.
+   * @return The predicate containing a single ? bind parameter which will be bound to the 'as at' timestamp value
+   */
   public String getAsOfPredicate(String asOfTableAlias, String asOfSysPeriod) {
     throw new RuntimeException("AsOf query not support of this database platform yet");
   }

src/main/java/com/avaje/ebean/config/dbplatform/Postgres8Platform.java

@@ -50,6 +50,21 @@ public class Postgres8Platform extends DatabasePlatform {
 
   }
 
+  /**
+   * Build and return the 'as of' predicate for a given table alias.
+   * <p>
+   * Each @History entity involved in the query has this predicate added using the related table alias.
+   * </p>
+   */
+  public String getAsOfPredicate(String asOfTableAlias, String asOfSysPeriod) {
+
+    // for Postgres we are using the 'timestamp with timezone range' data type
+    // as our sys_period column so hence the predicate below
+    StringBuilder sb = new StringBuilder(40);
+    sb.append(asOfTableAlias).append(".").append(asOfSysPeriod).append(" @> ?::timestamptz");
+    return sb.toString();
+  }
+
   /**
    * Create a Postgres specific sequence IdGenerator.
    */

src/main/java/com/avaje/ebean/config/dbplatform/PostgresPlatform.java

@@ -68,6 +68,8 @@ public class PostgresPlatform extends DatabasePlatform {
    */
   public String getAsOfPredicate(String asOfTableAlias, String asOfSysPeriod) {
 
+    // for Postgres we are using the 'timestamp with timezone range' data type
+    // as our sys_period column so hence the predicate below
     StringBuilder sb = new StringBuilder(40);
     sb.append(asOfTableAlias).append(".").append(asOfSysPeriod).append(" @> ?::timestamptz");
     return sb.toString();