39.7 The Freeze Catalog

In each database environment, Freeze maintains an internal table that contains type information describing all the databases in the environment. This table is an instance of a Freeze map in which the key is a string representing the database name and the value is an instance of Freeze::CatalogData:

module Freeze {
    struct CatalogData {
        bool evictor;
        string key;
        string value;
    };
};

An entry describes an evictor database if the evictor member is true, in which case the key and value members are empty strings. An entry that describes a Freeze map sets evictor to false; the key and value members contain the Slice types used when the map was defined.

Tools such as transformdb and dumpdb (see Chapter 40) access the catalog to obtain type information when none is supplied by the user. You can also use dumpdb to display the catalog of a database environment.

Freeze applications may access the catalog in the same manner as any other Freeze map. For example, the following C++ code displays the contents of a catalog:

#include <Freeze/Catalog.h>
...
string envName = ...;
Freeze::ConnectionPtr conn =
    Freeze::createConnection(communicator, envName);
Freeze::Catalog catalog(conn, Freeze::catalogName());
for (Freeze::Catalog::const_iterator p = catalog.begin();
    p != catalog.end(); ++p) {
    if (p‑>second.evictor)
        cout << p‑>first << ": evictor" << endl;
    else
        cout << p‑>first << ": map<" << p‑>second.key
             << ", " << p‑>second.value << ">" << endl;
}
conn‑>close();

The equivalent Java code is shown below:

String envName = ...;
Freeze.Connection conn =
    Freeze.Util.createConnection(communicator, envName);
Freeze.Catalog catalog =
    new Freeze.Catalog(conn, Freeze.Util.catalogName(), true);
for (java.util.Map.Entry<String, Freeze.CatalogData> e :
     catalog.entrySet()) {
    String name = e.getKey();
    Freeze.CatalogData data = e.getValue();
    if (data.evictor)
        System.out.println(name + ": evictor");
    else
        System.out.println(name + ": map<" + data.key + ", " +
                           data.value + ">");
}
conn.close();