CS27020 Object Relational Mapping and a Persistence Layer PDF

Object Relational Mapping and a Persistence Layer O-R Mapping Integration with high level languages Building applications with persistent storage Praboda Rajapaksha...

Object Relational Mapping and a Persistence Layer O-R Mapping Integration with high level languages Building applications with persistent storage Praboda Rajapaksha (with credit to Nigel Hardy) Modelling Persistent Data CS27020 Computer Science Department 1 / 31 Object Relational Mapping and a Persistence Layer O-R Mapping Last time Introduction Started to look at JDBC as an example of a CLI Did not see handling of the responses from the DBMS 2 / 31 Object Relational Mapping and a Persistence Layer O-R Mapping The ResultSet object Has metadata resultSet.getMetaData() an object that can be used to get information about the types and properties of the columns in a ResultSet object. access methods to describe the set, include: details of the column headers can the result set be re-read (scroll back) Has a concept of “current record” Initially the cursor is positioned before the first row..next and (probably) a range of methods to move the “cursor” to the next row and can use a while loop to iterate over has get methods for named and indexed fields can get fields as a wide range of types (if they convert) The SQL ordered list is mapped as a Java iterable collection a special type (class) not a domain specific type 3 / 31 Object Relational Mapping and a Persistence Layer O-R Mapping Accessing the ResultSet ResultSet resultSet = statement. executeQuery ( " s e l e c t ∗ from e l e c t e d m a y o r s " ) ; R e s u l t S e t M e t a D a t a metaData = r e s u l t S e t. getMetaData ( ) ; 4 / 31 Object Relational Mapping and a Persistence Layer O-R Mapping The metadata i n t c o l s = metaData. getColumnCount ( ) ; for ( int i = 1 ; i