5 Metadata

Example 5-1 How to Obtain Metadata About Attributes of a Simple Database Table

The following code example demonstrates how to obtain metadata about attributes of a simple database table:

/* Create an environment and a connection to the HR database */
.
.
/* Call the getMetaData method on the Connection object obtainedv*/
MetaData emptab_metaData = connection->getMetaData(
      "EMPLOYEES", MetaData::PTYPE_TABLE);
/* Now that you have the metadata information on the EMPLOYEES table,
   call the getxxx methods using the appropriate attributes */

/* Call getString */
cout<<"Schema:"<<(emptab_metaData.getString(MetaData::ATTR_OBJ_SCHEMA))<<endl;

if(emptab_metaData.getInt(emptab_metaData::ATTR_PTYPE)==MetaData::PTYPE_TABLE)
   cout<<"EMPLOYEES is a table"<<endl;
else
    cout<<"EMPLOYEES is not a table"<<endl;

/* Call getInt to get the number of columns in the table */
int columnCount=emptab_metaData.getInt(MetaData::ATTR_NUM_COLS);
cout<<"Number of Columns:"<<columnCount<<endl;

/* Call getTimestamp to get the timestamp of the table object */
Timestamp tstamp = emptab_metaData.getTimestamp(MetaData::ATTR_TIMESTAMP);
/* Now that you have the value of the attribute as a Timestamp object,
   you can call methods to obtain the components of the timestamp */
int year;
unsigned int month, day;
tstamp.getData(year, month, day);

/* Call getVector for attributes of list type,for example ATTR_LIST_COLUMNS */
vector<MetaData>listOfColumns;
listOfColumns=emptab_metaData.getVector(MetaData::ATTR_LIST_COLUMNS);

/* Each of the list elements represents a column metadata,
   so now you can access the column attributes*/
for (int i=0;i<listOfColumns.size();i++
{
   MetaData columnObj=listOfColumns[i];
   cout<<"Column Name:"<<(columnObj.getString(MetaData::ATTR_NAME))<<endl;
   cout<<"Data Type:"<<(columnObj.getInt(MetaData::ATTR_DATA_TYPE))<<endl;
   .
   .
   /* and so on to obtain metadata on other column specific attributes */
}

Example 5-2 How to Obtain Metadata from a Column Containing User Defined Types

/* Create an environment and a connection to the HR database */
...
/* Call the getMetaData method on the Connection object obtained */
MetaData custtab_metaData = connection->getMetaData(
      "CUSTOMERS", MetaData::PTYPE_TABLE);

/* Have metadata information on the CUSTOMERS table; call the getxxx methods */
/* Call getString */
cout<<"Schema:"<<(custtab_metaData.getString(MetaData::ATTR_OBJ_SCHEMA))<<endl;
if(custtab_metaData.getInt(custtab_metaData::ATTR_PTYPE)==MetaData::PTYPE_TABLE)
   cout<<"CUSTOMERS is a table"<<endl;
else
   cout<<"CUSTOMERS is not a table"<<endl;

/* Call getVector to obtain list of columns in the CUSTOMERS table */
vector<MetaData>listOfColumns;
listOfColumns=custtab_metaData.getVector(MetaData::ATTR_LIST_COLUMNS);

/* Assuming metadata for column cust_address_typ is fourth element in list*/
MetaData customer_address=listOfColumns[3];

/* Obtain the metadata for the customer_address attribute */
int typcode = customer_address.getInt(MetaData::ATTR_TYPECODE);
if(typcode==OCCI_TYPECODE_OBJECT)
   cout<<"customer_address is an object type"<<endl;
else
   cout<<"customer_address is not an object type"<<endl;

string objectName=customer_address.getString(MetaData::ATTR_OBJ_NAME);

/* Now that you have the name of the address object,
   the metadata of the attributes of the type can be obtained by using
   getMetaData on the connection by passing the object name
*/
MetaData address = connection->getMetaData(objectName);

/* Call getVector to obtain the list of the address object attributes */
vector<MetaData> attributeList = 
      address.getVector(MetaData::ATT_LIST_TYPE_ATTRS);

/* and so on to obtain metadata on other address object specific attributes */

Example 5-3 How to obtain object metadata from a reference

The following code example demonstrates how to obtain metadata about an object when using a reference to it:

Assuming the following schema structure:

Type ADDRESS(street VARCHAR2(50), city VARCHAR2(20));
Table Person(id NUMBER, addr REF ADDRESS);

/* Create an environment and a connection to the HR database */
.
.
/* Call the getMetaData method on the Connection object obtained */
MetaData perstab_metaData = connection->getMetaData(
      "Person", MetaData::PTYPE_TABLE);

/* Now that you have the metadata information on the Person table,
   call the getxxx methods using the appropriate attributes */
/* Call getString */
cout<<"Schema:"<<(perstab_metaData.getString(MetaData::ATTR_OBJ_SCHEMA))<<endl;

if(perstab_metaData.getInt(perstab_metaData::ATTR_PTYPE)==MetaData::PTYPE_TABLE)
   cout<<"Person is a table"<<endl;
else
   cout<<"Person is not a table"<<endl;

/* Call getVector to obtain the list of columns in the Person table*/
vector<MetaData>listOfColumns;
listOfColumns=perstab_metaData.getVector(MetaData::ATTR_LIST_COLUMNS);

/* Each of the list elements represents a column metadata,
   so now get the datatype of the column by passing ATTR_DATA_TYPE
   to getInt */
for(int i=0;i<numCols;i++)
{
   int dataType=colList[i].getInt(MetaData::ATTR_DATA_TYPE);
   /* If the datatype is a reference, get the Ref and obtain the metadata
      about the object by passing the Ref to getMetaData */
   if(dataType==SQLT_REF)
      RefAny refTdo=colList[i].getRef(MetaData::ATTR_REF_TDO);

   /* Now you can obtain the metadata about the object as shown
   MetaData tdo_metaData=connection->getMetaData(refTdo);

   /* Now that you have the metadata about the TDO, you can obtain the metadata
      about the object */
}

Example 5-4 How to Obtain Metadata About a Select List from a ResultSet Object

/* Create an environment and a connection to the database */
...
/* Create a statement and associate it with a select clause */
string sqlStmt="SELECT * FROM EMPLOYEES";
Statement *stmt=conn->createStatement(sqlStmt);

/* Execute the statement to obtain a ResultSet */
ResultSet *rset=stmt->executeQuery();

/* Obtain the metadata about the select list */
vector<MetaData>cmd=rset->getColumnListMetaData();

/* The metadata is a column list and each element is a column metaData */
int dataType=cmd[i].getInt(MetaData::ATTR_DATA_TYPE);
...

The getMetaData method is called for the ATTR_COLLECTION_ELEMENT attribute only.