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DataSources.html
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<!DOCTYPE html>
<!--
| Generated by Apache Maven Doxia Site Renderer 1.7.4 at 2021-09-25
| Rendered using Apache Maven Fluido Skin 1.5
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<title>JDBDT – Data sources</title>
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<li id="publishDate">Last Published: 2021-09-25
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<h1>Data sources</h1>
<p><tt>DataSource</tt> objects represent tables and queries that are used for database <a href="DBSetup.html">setup</a> or <a href="DBAssertions.html">assertions</a>.</p>
<p><a name="Table"></a></p>
<div class="section">
<h2><a name="Tables"></a>Tables</h2>
<p><a name="Table_Builder"></a></p>
<div class="section">
<h3><a name="Using_table_builders"></a>Using table builders</h3>
<p>Tables are represented by <tt>Table</tt>, a subclass of <tt>DataSource</tt>. A table is created using a builder (<tt>TableBuilder</tt>), as returned by the <tt>table</tt> facade method. In association, the <tt>columns</tt> should be used to specify the table columns of interest, and the <tt>build</tt> method to build the actual <tt>Table</tt> object in association to a <a href="DB.html">database handle</a>.</p>
<p><i>Illustration</i></p>
<div class="source">
<div class="source"><pre class="prettyprint">import static org.jdbdt.JDBDT.*;
import org.jdbdt.DB;
import org.jdbdt.Table;
...
DB db = ...;
Table userTable = table("USER")
.columns("LOGIN", "NAME", "PASSWORD", "CREATED")
.build(db);
</pre></div></div>
<p><a name="Table_Key"></a></p></div>
<div class="section">
<h3><a name="Key_columns_for_a_table"></a>Key columns for a table</h3>
<p>In addition, if you wish to perform updates and deletes using data sets, <tt>key</tt> can be used to define the columns that form the table’s primary key (or that in some other form identify each database row uniquely) </p>
<p><i>Illustration</i></p>
<div class="source">
<div class="source"><pre class="prettyprint"> Table userTable = table("USER")
.columns("LOGIN", "NAME", "PASSWORD", "CREATED")
.key("LOGIN")
.build(db);
</pre></div></div>
<p><a name="Query"></a></p></div></div>
<div class="section">
<h2><a name="Queries"></a>Queries</h2>
<p>Queries are represented by <tt>Query</tt>, a subclass of <tt>DataSource</tt>. A <tt>Query</tt> object can be created from a raw SQL statements or using a <tt>QueryBuilder</tt>. </p>
<p><a name="RawQuery"></a></p>
<div class="section">
<h3><a name="Definition_from_raw_SQL"></a>Definition from raw SQL</h3>
<p>The <tt>query</tt> facade method may be used to define a query using raw SQL.</p>
<p><i>Illustration</i></p>
<div class="source">
<div class="source"><pre class="prettyprint">import static org.jdbdt.JDBDT.*;
import org.jdbdt.DB;
import org.jdbdt.Query;
...
DB db = ...;
// Query user login and name by id.
int idArgument = ...;
Query q = query(db, "SELECT LOGIN, NAME FROM USER WHERE ID = ?", idArgument);
</pre></div></div>
<p><a name="QueryBuilder"></a></p></div>
<div class="section">
<h3><a name="Definition_using_QueryBuilder"></a>Definition using <tt>QueryBuilder</tt></h3>
<p><tt>QueryBuilder</tt> objects can be used to define queries programmatically. The <tt>select</tt> facade method creates a query builder that can be parameterized using a chained sequence of calls. A final call to <tt>build</tt> in such a sequence creates a <tt>Query</tt> object for a given database. The parameterization methods are the following:</p>
<ul>
<li><tt>from</tt>: defines the <tt>FROM</tt> clause;</li>
<li><tt>where</tt>: defines a <tt>WHERE</tt> clause;</li>
<li><tt>distinct</tt>: defines a <tt>DISTINCT</tt> modifier for the query;</li>
<li><tt>groupBy</tt>: defines a <tt>GROUP BY</tt> clause;</li>
<li><tt>having</tt>: defines a <tt>HAVING</tt> clause;</li>
<li><tt>orderBy</tt>: defines an <tt>ORDER BY</tt> clause;</li>
<li><tt>limit</tt>: defines a <tt>LIMIT</tt> clause;</li>
<li><tt>arguments</tt>: supply arguments for the query.</li>
</ul>
<p>Note to <tt>orderBy</tt>: <a href="DBAssertions.html">database assertions</a> are insensitive to the order of query results, but the use of <tt>orderBy</tt> may make it easier to inspect <a href="Logs.html">logs</a> in some cases.</p>
<p><i>Illustration</i></p>
<div class="source">
<div class="source"><pre class="prettyprint">import static org.jdbdt.JDBDT.*;
import org.jdbdt.DB;
import org.jdbdt.Query;
...
DB db = ...;
// [1] Query user login and name by id
int userId = ...;
Query q1 = select("LOGIN", "NAME")
.from("USER")
.where("ID = ?")
.arguments(userId)
.build(db);
// [2] Query distinct passwords in use
Query q2 = select("PASSWORD")
.distinct()
.from("USER")
.orderBy("PASSWORD")
.build(db);
// [3] Get passwords that are used by more than one user and their count.
Query q3 = select("PASSWORD", "COUNT(*)")
.from("USER")
.groupBy("PASSWORD")
.having("COUNT(*) > 1")
.build(db);
// [4] Get pairs of users that have the same password.
Query q4 = select("u1.LOGIN", "u2.LOGIN")
.from("USER u1", "USER u2")
.where("u1.LOGIN <> u2.LOGIN AND u1.PASSWORD = u2.PASSWORD")
.build(db);
</pre></div></div>
<p><a name="SummaryOfMethods"></a></p></div></div>
<div class="section">
<h2><a name="Summary_of_API_methods"></a>Summary of API methods</h2>
<div class="section">
<h3><a name="JDBDT"></a><tt>JDBDT</tt></h3>
<ul>
<li><tt>table(name)</tt> creates a new <tt>TableBuilder</tt> with table name set to <tt>name</tt>.</li>
<li><tt>query(db, sql [,args])</tt> creates a new <tt>Query</tt> data source from SQL code.</li>
<li><tt>select(cols)</tt> creates a new <tt>QueryBuilder</tt> with columns set to <tt>cols</tt>.</li>
</ul></div>
<div class="section">
<h3><a name="DataSource"></a><tt>DataSource</tt></h3>
<ul>
<li><tt>getDB()</tt> returns the database handle.</li>
<li><tt>getSQLForQuery()</tt> yields the SQL code used for querying the database.</li>
<li><tt>getColumnCount()</tt> returns the number of columns for the data source.</li>
<li><tt>getColumns()</tt> returns the list of columns.</li>
<li><tt>getColumnName(i)</tt> returns the name of the column with index <tt>i</tt>.</li>
</ul></div>
<div class="section">
<h3><a name="Table"></a><tt>Table</tt></h3>
<ul>
<li><tt>getName()</tt> returns the table name.</li>
</ul></div>
<div class="section">
<h3><a name="TableBuilder"></a><tt>TableBuilder</tt></h3>
<ul>
<li><tt>columns(cols)</tt> set the table columns to cols.</li>
<li><tt>key(cols)</tt> set the key columns to consider (optional).</li>
<li><tt>name(t)</tt> sets the table name to <tt>t</tt>.</li>
<li><tt>build(db)</tt> builds the desired <tt>Table</tt> for database <tt>db</tt>.</li>
</ul></div>
<div class="section">
<h3><a name="QueryBuilder"></a><tt>QueryBuilder</tt></h3>
<ul>
<li><tt>columns(cols)</tt> sets the query columns to <tt>cols</tt>.</li>
<li><tt>from</tt>, <tt>where</tt>, <tt>distinct</tt>, <tt>groupBy</tt>, <tt>having</tt>, <tt>orderBy</tt>, <tt>limit</tt>, <tt>arguments</tt>: query parameterization methods (see <a href="DataSources.html#QueryBuilder">above</a>).</li>
<li><tt>build(db)</tt> builds the desired <tt>Query</tt> for database <tt>db</tt>.</li>
</ul></div></div>
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