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| <h3>JDOQL</h3> |
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| <div class="sect1"> |
| <h2 id="JDOQL">JDOQL</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>JDO defines ways of querying objects persisted into the datastore. |
| It provides its own object-based query language (JDOQL). |
| JDOQL is designed as the Java developers way of having the power of SQL queries, yet retaining the Java object relationship that exist in their application model. |
| A typical JDOQL query may be set up in one of 2 ways. Here’s an example.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Declarative JDOQL :</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="predefined-type">Query</span> q = pm.newQuery(mydomain.Person.class, <span class="string"><span class="delimiter">"</span><span class="content">lastName == </span><span class="char">\"</span><span class="content">Jones</span><span class="char">\"</span><span class="content"> && age < age_limit</span><span class="delimiter">"</span></span>); |
| q.declareParameters(<span class="string"><span class="delimiter">"</span><span class="content">double age_limit</span><span class="delimiter">"</span></span>); |
| <span class="predefined-type">List</span> results = (<span class="predefined-type">List</span>)q.execute(<span class="float">20.0</span>);</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Single-String JDOQL :</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="predefined-type">Query</span> q = pm.newQuery(<span class="string"><span class="delimiter">"</span><span class="content">SELECT FROM mydomain.Person WHERE lastName == </span><span class="char">\"</span><span class="content">Jones</span><span class="char">\"</span><span class="delimiter">"</span></span> + |
| <span class="string"><span class="delimiter">"</span><span class="content"> && age < :age_limit PARAMETERS double age_limit</span><span class="delimiter">"</span></span>); |
| <span class="predefined-type">List</span> results = (<span class="predefined-type">List</span>)q.execute(<span class="float">20.0</span>);</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>So here in our example we select all "Person" objects with surname of "Jones" and where the persons age is below 20. |
| The language is intuitive for Java developers, and is intended as their interface to accessing the persisted data model. |
| As can be seen above, the query is made up of distinct parts. |
| The class being selected (the SELECT clause in SQL), the filter (which equates to the WHERE clause in SQL), |
| together with any sorting (the ORDER BY clause in SQL), etc.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Before giving details on JDOQL, you can download a quick reference guide <a href="jdoql_quickref.pdf">here</a></p> |
| </div> |
| <div class="sect2"> |
| <h3 id="singlestring">Single-String JDOQL</h3> |
| <div class="paragraph"> |
| <p>In original (declarative) JDOQL (JDO 1.0) it was necessary to specify the component parts (filter, candidate class, ordering, etc) |
| of the query using the mutator methods on the Query. From JDO 2 onwards you can specify it all in a single string. |
| This string has to follow a particular pattern, but provides the convenience that many people require. |
| The pattern to use is as follows</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>SELECT [UNIQUE] [<result>] [INTO <result-class>] |
| [FROM <candidate-class> [EXCLUDE SUBCLASSES]] |
| [WHERE <filter>] |
| [VARIABLES <variable declarations>] |
| [PARAMETERS <parameter declarations>] |
| [<import declarations>] |
| [GROUP BY <grouping>] |
| [ORDER BY <ordering>] |
| [RANGE <start>, <end>]</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>The "keywords" in the query are shown in UPPER CASE but can be in <em>UPPER</em> or <em>lower</em> case.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Lets give an example of a query using this syntax</p> |
| </div> |
| <div class="literalblock"> |
| <div class="content"> |
| <pre>SELECT UNIQUE FROM org.datanucleus.samples.Employee ORDER BY departmentNumber</pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>so we form the parts of the query as before, yet here we just specify it all in a single call.</p> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="Accessing_Fields">Accessing Fields</h3> |
| <div class="paragraph"> |
| <p>In JDOQL you access fields in the query by referring to the field name. |
| For example, if you are querying a class called <em>Product</em> and it has a field "price", then you access it like this</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="predefined-type">Query</span> query = pm.newQuery(mydomain.Product.class, <span class="string"><span class="delimiter">"</span><span class="content">price < 150.0</span><span class="delimiter">"</span></span>);</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>In addition to the persistent fields, you can also access "public static final" fields of any class. You can do this as follows</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="predefined-type">Query</span> query = pm.newQuery(mydomain.Product.class, <span class="string"><span class="delimiter">"</span><span class="content">taxPercent < mydomain.Product.TAX_BAND_A</span><span class="delimiter">"</span></span>);</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>So this will find all products that include a tax percentage less than some "BAND A" level. |
| Where you are using "public static final" fields you can either fully-qualify the class name or you can include it in the |
| "imports" section of the query (see later).</p> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="Data_types_:_literals">Data types : literals</h3> |
| <div class="paragraph"> |
| <p>JDOQL supports the following literals: IntegerLiteral, FloatingPointLiteral, BooleanLiteral, CharacterLiteral, StringLiteral, and NullLiteral.</p> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="Operators_precedence">Operators precedence</h3> |
| <div class="paragraph"> |
| <p>The following list describes the operator precedence in JDOQL.</p> |
| </div> |
| <div class="olist arabic"> |
| <ol class="arabic"> |
| <li> |
| <p>Cast</p> |
| </li> |
| <li> |
| <p>Unary ("~") ("!")</p> |
| </li> |
| <li> |
| <p>Unary ("+") ("-")</p> |
| </li> |
| <li> |
| <p>Multiplicative ("*") ("/") ("%")</p> |
| </li> |
| <li> |
| <p>Additive ("+") ("-")</p> |
| </li> |
| <li> |
| <p>Relational (">=") (">") ("⇐") ("<") ("instanceof")</p> |
| </li> |
| <li> |
| <p>Equality ("==") ("!=")</p> |
| </li> |
| <li> |
| <p>Boolean logical AND ("&")</p> |
| </li> |
| <li> |
| <p>Boolean logical OR ("|")</p> |
| </li> |
| <li> |
| <p>Conditional AND ("&&")</p> |
| </li> |
| <li> |
| <p>Conditional OR ("||")</p> |
| </li> |
| </ol> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="Concatenation_Expressions">Concatenation Expressions</h3> |
| <div class="paragraph"> |
| <p>The concatenation operator(+) concatenates a String to either another String or Number. |
| Concatenations of String or Numbers to null results in null.</p> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="Example_1_-_Use_of_Explicit_Parameters">Example 1 - Use of Explicit Parameters</h3> |
| <div class="paragraph"> |
| <p>Here’s a simple example for finding the elements of a class with a field below a particular threshold level. |
| Here we pass in the threshold value (<em>limit</em>), and sort the output in order of ascending price.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Declarative JDOQL :</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="predefined-type">Query</span> query = pm.newQuery(mydomain.Product.class,<span class="string"><span class="delimiter">"</span><span class="content">price < limit</span><span class="delimiter">"</span></span>); |
| query.declareParameters(<span class="string"><span class="delimiter">"</span><span class="content">double limit</span><span class="delimiter">"</span></span>); |
| query.setOrdering(<span class="string"><span class="delimiter">"</span><span class="content">price ascending</span><span class="delimiter">"</span></span>); |
| <span class="predefined-type">List</span> results = (<span class="predefined-type">List</span>)query.execute(<span class="float">150.00</span>);</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Single-String JDOQL :</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="predefined-type">Query</span> query = pm.newQuery(<span class="string"><span class="delimiter">"</span><span class="content">SELECT FROM mydomain.Product WHERE </span><span class="delimiter">"</span></span> + |
| <span class="string"><span class="delimiter">"</span><span class="content">price < limit PARAMETERS double limit ORDER BY price ASCENDING</span><span class="delimiter">"</span></span>); |
| <span class="predefined-type">List</span> results = (<span class="predefined-type">List</span>)query.execute(<span class="float">150.00</span>);</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>For completeness, the class is shown here</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="type">class</span> <span class="class">Product</span> |
| { |
| <span class="predefined-type">String</span> name; |
| <span class="type">double</span> price; |
| java.util.Date endDate; |
| ... |
| }</code></pre> |
| </div> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="xml"><span class="tag"><jdo></span> |
| <span class="tag"><package</span> <span class="attribute-name">name</span>=<span class="string"><span class="delimiter">"</span><span class="content">mydomain</span><span class="delimiter">"</span></span><span class="tag">></span> |
| <span class="tag"><class</span> <span class="attribute-name">name</span>=<span class="string"><span class="delimiter">"</span><span class="content">Product</span><span class="delimiter">"</span></span><span class="tag">></span> |
| <span class="tag"><field</span> <span class="attribute-name">name</span>=<span class="string"><span class="delimiter">"</span><span class="content">name</span><span class="delimiter">"</span></span><span class="tag">></span> |
| <span class="tag"><column</span> <span class="attribute-name">length</span>=<span class="string"><span class="delimiter">"</span><span class="content">100</span><span class="delimiter">"</span></span> <span class="attribute-name">jdbc-type</span>=<span class="string"><span class="delimiter">"</span><span class="content">VARCHAR</span><span class="delimiter">"</span></span><span class="tag">/></span> |
| <span class="tag"></field></span> |
| <span class="tag"><field</span> <span class="attribute-name">name</span>=<span class="string"><span class="delimiter">"</span><span class="content">abreviation</span><span class="delimiter">"</span></span><span class="tag">></span> |
| <span class="tag"><column</span> <span class="attribute-name">length</span>=<span class="string"><span class="delimiter">"</span><span class="content">20</span><span class="delimiter">"</span></span> <span class="attribute-name">jdbc-type</span>=<span class="string"><span class="delimiter">"</span><span class="content">VARCHAR</span><span class="delimiter">"</span></span><span class="tag">/></span> |
| <span class="tag"></field></span> |
| <span class="tag"><field</span> <span class="attribute-name">name</span>=<span class="string"><span class="delimiter">"</span><span class="content">price</span><span class="delimiter">"</span></span><span class="tag">/></span> |
| <span class="tag"><field</span> <span class="attribute-name">name</span>=<span class="string"><span class="delimiter">"</span><span class="content">endDate</span><span class="delimiter">"</span></span><span class="tag">/></span> |
| <span class="tag"></class></span> |
| <span class="tag"></package></span> |
| <span class="tag"></jdo></span></code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p><br></p> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="Example_2_-_Use_of_Implicit_Parameters">Example 2 - Use of Implicit Parameters</h3> |
| <div class="paragraph"> |
| <p>Let’s repeat the previous query but this time using <em>implicit</em> parameters.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Declarative JDOQL :</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="predefined-type">Query</span> query = pm.newQuery(mydomain.Product.class,<span class="string"><span class="delimiter">"</span><span class="content">price < :limit</span><span class="delimiter">"</span></span>); |
| query.setOrdering(<span class="string"><span class="delimiter">"</span><span class="content">price ascending</span><span class="delimiter">"</span></span>); |
| <span class="predefined-type">List</span> results = (<span class="predefined-type">List</span>)query.execute(<span class="float">150.00</span>);</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Single-String JDOQL :</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="predefined-type">Query</span> query = pm.newQuery(<span class="string"><span class="delimiter">"</span><span class="content">SELECT FROM mydomain.Product WHERE </span><span class="delimiter">"</span></span> + |
| <span class="string"><span class="delimiter">"</span><span class="content">price < :limit ORDER BY price ASCENDING</span><span class="delimiter">"</span></span>); |
| <span class="predefined-type">List</span> results = (<span class="predefined-type">List</span>)query.execute(<span class="float">150.00</span>);</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>So we omitted the declaration of the parameter and just prefixed it with a colon (:).</p> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="Example_3_-_Comparison_against_Dates">Example 3 - Comparison against Dates</h3> |
| <div class="paragraph"> |
| <p>Here’s another example using the same Product class as above, but this |
| time comparing to a Date field. Because we are using a type in our |
| query, we need to <em>import</em> it …​ just like you would in a Java class if |
| you were using it there.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Declarative JDOQL :</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="predefined-type">Query</span> query = pm.newQuery(domain.Product.class, |
| <span class="string"><span class="delimiter">"</span><span class="content">endDate > best_before_limit</span><span class="delimiter">"</span></span>); |
| query.declareImports(<span class="string"><span class="delimiter">"</span><span class="content">import java.util.Date</span><span class="delimiter">"</span></span>); |
| query.declareParameters(<span class="string"><span class="delimiter">"</span><span class="content">Date best_before_limit</span><span class="delimiter">"</span></span>); |
| query.setOrdering(<span class="string"><span class="delimiter">"</span><span class="content">endDate descending</span><span class="delimiter">"</span></span>); |
| <span class="predefined-type">Collection</span> results = (<span class="predefined-type">Collection</span>)query.execute(my_date_limit);</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Single-String JDOQL :</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="predefined-type">Query</span> query = pm.newQuery(<span class="string"><span class="delimiter">"</span><span class="content">SELECT FROM mydomain.Product </span><span class="delimiter">"</span></span> + |
| <span class="string"><span class="delimiter">"</span><span class="content">WHERE endDate > best_before_limit </span><span class="delimiter">"</span></span> + |
| <span class="string"><span class="delimiter">"</span><span class="content">PARAMETERS Date best_before_limit </span><span class="delimiter">"</span></span> + |
| <span class="string"><span class="delimiter">"</span><span class="content">import java.util.Date ORDER BY endDate DESC</span><span class="delimiter">"</span></span>); |
| <span class="predefined-type">List</span> results = (<span class="predefined-type">List</span>)query.execute(my_date_limit);</code></pre> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="Example_4_-_Instanceof">Example 4 - Instanceof</h3> |
| <div class="paragraph"> |
| <p>This example demonstrates use of the "instanceof" operator. |
| We have a class A that has a field "b" of type B and B has subclasses B1, B2, B3. |
| Clearly the field "b" of A can be of type B, B1, B2, B3 etc, and we want to find all objects of type A that have the field "b" that is of type B2. |
| We do it like this</p> |
| </div> |
| <div class="paragraph"> |
| <p>Declarative JDOQL :</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="predefined-type">Query</span> query = pm.newQuery(mydomain.A.class); |
| query.setFilter(<span class="string"><span class="delimiter">"</span><span class="content">b instanceof mydomain.B2</span><span class="delimiter">"</span></span>); |
| <span class="predefined-type">List</span> results = (<span class="predefined-type">List</span>)query.execute();</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Single-String JDOQL :</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="predefined-type">Query</span> query = pm.newQuery(<span class="string"><span class="delimiter">"</span><span class="content">SELECT FROM mydomain.A WHERE b instanceof mydomain.B2</span><span class="delimiter">"</span></span>); |
| <span class="predefined-type">List</span> results = (<span class="predefined-type">List</span>)query.execute();</code></pre> |
| </div> |
| </div> |
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