Data sets

A DataSet object represents a collection of rows for a data source that may be used for database setup or assertions.

Creation

The examples below define data sets for a table (Table) object, but the definition of data sets works similarly for queries (Query).

Plain definition

In the simplest manner, DataSet objects are created through the data JDBDT facade method, typically followed by a chained sequence of calls.

Illustration

import static org.jdbdt.JDBDT.*;
import org.jdbdt.DataSet;
import org.jdbdt.DB;
import org.jdbdt.Table;
...
DB db = ...;
Table t = table("USERS")
         .columns("ID", "LOGIN", "NAME", "PASSWORD", "CREATED")
         .build(db);

DataSet users
   = data(t)
    .row(0,   "root",  "Root User",  "god",       null)
    .row(101, "john",  "John Doe",   "justDoeIt", Date.valueOf("2014-07-12"))
    .row(102, "harry", "Harry H",    "meta",      Date.valueOf("2016-01-01"))
    .row(103, "guest", "Guest User", "welcome",   Date.valueOf("2016-01-02"));

Typed data sets

TypedDataSet is a typed extension of DataSet. It allows for a simple form of (one-way) object-relational mapping through conversion functions expressed by the Conversion interface. A Conversion instance defines a mapping from objects to rows, where each row is expressed as an array of column values.

Illustration

import static org.jdbdt.JDBDT.*;
import org.jdbdt.TypedDataSet;
import org.jdbdt.DB;
import org.jdbdt.Table;
...
DB db = ...;
Table t = table("USERS")
         .columns("ID", "LOGIN", "NAME", "PASSWORD", "CREATED")
         .build(db);

Conversion<User> conv = u -> new Object[] {  
                          u.getID(), 
                          u.getLogin(),
                          u.getPassword(),
                          u.getCreationDate() 
                        };
User root = ..., john = ..., harry = ..., guest = ...;
List<User> listOfOtherUsers ...;  

TypedDataSet<User> userSet  
   = data(t, conv)
    .row(root)
    .rows(john, harry, guest)
    .rows(listOfOtherUsers);

Data set builders

A DataSetBuilder instance can be used to define or augment a data set with the aid of expressive column filler methods. For instance, there are column fillers for value sequences or pseudo-random values. Many of the column fillers may be defined concisely, for example making use of lambda expressions, arrays, or collections.

The builder facade method creates a builder for a fresh data set and the DataSet.build method lets you add rows to a previously defined data set.

Illustration

import static org.jdbdt.JDBDT.*;
import org.jdbdt.DB;
import org.jdbdt.Table;
import org.jdbdt.DataSet;
...
DB db = ...;
Table t = table("USERS")
         .columns("ID", "LOGIN", "NAME", "PASSWORD", "CREATED")
         .build(db);    

// Create a fresh data set with 9 rows
DataSet data = 
   builder(t)
  .sequence("ID", 1) // 1, 2, 3, ...
  .sequence("LOGIN", "harry", "mark", "john")
  .sequence("NAME", "Harry H", "Mark M", "John J")
  .sequence("PASSWORD", i -> "password " + i , 1)
  .random("CREATED", Date.valueOf("2015-01-01"), Date.valueOf("2015-12-31"))
  .generate(3) // generate 3 rows, 
  .sequence("LOGIN", i -> "guest_" + i, 4)  // "user_4", "user_5", ...
  .sequence("NAME", i -> "Guest User " + i, 4) // "Guest User 4", ...
  .value("password", "samePasswordForAllGuests") 
  .generate(6) // 6 more rows keeping ID sequence and CREATED random filler
  .data();   

// Add 500 more rows to the data set
data.build()
    .sequence("ID", 1000) // 1000, 1001, ... 
    .sequence("LOGIN", i -> "anotherUser" + i, 1000)
    .sequence("NAME", i -> "Yet Another User" + i, 1000)
    .random("PASSWORD", "aeiou", "qwerty", "12345", "pass is the password")
    .nullValue("CREATED") // set to NULL
    .generate(500);

Read-only data sets

A data set is marked read-only when defined as a database snapshot. Any attempt to modify it subsequently will cause an InvalidOperationException.

Summary of API methods

JDBDT

Object creation - for a data source s:

  • data(s) creates a new data set.
  • data(s, c) creates a new typed data set with conversion function c.
  • builder(s) creates a data set builder with an underlying fresh data set.
  • empty(s) returns an empty & read-only data set that is unique for s.

Debugging:

  • dump(s, out) dump database contents of data source s to stream/file out.
  • dump(data, out) dump the contents of data set data to stream/file out.

DataSet, TypedDataSet

Properties:

  • size() returns the number of rows.
  • isEmpty() indicates if the data set is empty.
  • isReadOnly() indicates if the data set is read-only.
  • getDataSource() returns the data source instance for the data set.

Mutators:

  • row and rows methods add rows to the data set (see examples above).
  • build() creates a new data set builder backed up by the data set (see example above).
  • add(other) adds all rows from other to the data set.
  • setReadOnly() sets the data set as read-only.

Utility methods (all static):

  • copyOf(data) returns a new data set that has the same rows as data.
  • join(data1, data2, ...,) returns a new data set that contains all the rows in data1, data2, …
  • subset(data, index, n) returns a new data set containing n rows of data starting from the index-th row.
  • singleton(data, i) returns a new data set containing only the index-th row in data.
  • first(data, n) returns a new data set containing the first n rows of data.
  • last(data, n) returns a new data set containing the last n rows of data.

DataSetBuilder

  • data() returns the underlying data set.
  • generate(n) adds n rows to the underlying data set based on the current column filler settings.
  • value(column, v) sets a constant filler with value v for column.
  • nullValue(column) sets a NULL value filler for column.
  • remainingColumnsNull() sets the NULL value filler for all remaining columns
  • allColumnsNull() sets the NULL value filler for all columns
  • sequence(column, ...) defines a sequence fillers for column (several method variants).
  • random(column, ...) defines a pseudo-random filler for column (several method variants).
  • set(column, filler) defines a custom column filler for column.