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| <h1 class="content-header header-section1" id="pgui_datamodel_scalar" itemprop="headline">Scalars</h1> |
| </div></div><p>There are 4 scalar types:</p><ul> |
| <li> |
| Boolean |
| </li> |
| |
| <li> |
| Number |
| </li> |
| |
| <li> |
| String |
| </li> |
| |
| <li> |
| Date |
| </li> |
| </ul><p>For each scalar type is a |
| <code class="inline-code">Template<em class="code-color">Type</em>Model</code> |
| interface, where <code class="inline-code"><em class="code-color">Type</em></code> is |
| the name of the type. These interfaces define only one method: |
| <code class="inline-code"><em class="code-color">type</em> |
| getAs<em class="code-color">Type</em>();</code>. This returns the |
| value of the variable with the Java type (<code class="inline-code">boolean</code>, |
| <code class="inline-code">Number</code>, <code class="inline-code">String</code> and |
| <code class="inline-code">Date</code> respectively).</p> <div class="callout note"> |
| <strong class="callout-label">Note:</strong> |
| |
| <p>For historical reasons the interface for string scalars is |
| called <code class="inline-code">TemplateScalarModel</code>, not |
| <code class="inline-code">TemplateStringModel</code>.</p> |
| </div> |
| <p>A trivial implementation of these interfaces are available in |
| <code class="inline-code">freemarker.template</code> package with |
| <code class="inline-code">Simple<em class="code-color">Type</em></code> class name. |
| However, there is no <code class="inline-code">SimpleBooleanModel</code>; to |
| represent the boolean values you can use the |
| <code class="inline-code">TemplateBooleanModel.TRUE</code> and |
| <code class="inline-code">TemplateBooleanModel.FALSE</code> singletons.</p> <div class="callout note"> |
| <strong class="callout-label">Note:</strong> |
| |
| <p>For historical reasons the class for string scalars is called |
| <code class="inline-code">SimpleScalar</code>, not |
| <code class="inline-code">SimpleString</code>.</p> |
| </div> |
| <p>Scalars are immutable within FTL. When you set the value of a |
| variable in a template, then you replace the |
| <code class="inline-code">Template<em class="code-color">Type</em>Model</code> |
| instance with another instance, and don't change the value stored in |
| the original instance.</p> |
| |
| |
| |
| |
| <h2 class="content-header header-section2" id="autoid_31">Difficulties with the date type</h2> |
| |
| |
| |
| |
| |
| |
| <p>There is a complication around date types, because Java API |
| usually does not differentiate <code class="inline-code">java.util.Date</code>-s |
| that store only the date part (April 4, 2003), only the time part |
| (10:19:18 PM), or both (April 4, 2003 10:19:18 PM). To display a |
| date variable as text correctly, FreeMarker must know what parts of |
| the <code class="inline-code">java.util.Date</code> stores meaningful information, |
| and what parts are unused. Unfortunately, the only place where the |
| Java API cleanly tells this, is with database handling (SQL), |
| because databases typically has separated date, time and timestamp |
| (aka date-time) types, and <code class="inline-code">java.sql</code> has 3 |
| corresponding <code class="inline-code">java.util.Date</code> subclasses for |
| them.</p> |
| |
| <p><code class="inline-code">TemplateDateModel</code> interface has two |
| methods: <code class="inline-code">java.util.Date getAsDate()</code> and |
| <code class="inline-code">int getDateType()</code>. A typical implementation of |
| this interface, stores a <code class="inline-code">java.util.Date</code> object, |
| plus an integer that tells the "database style type". The value of |
| this integer must be a constant from the |
| <code class="inline-code">TemplateDateModel</code> interface: |
| <code class="inline-code">DATE</code>, <code class="inline-code">TIME</code>, |
| <code class="inline-code">DATETIME</code> and <code class="inline-code">UNKNOWN</code>.</p> |
| |
| <p>What is <code class="inline-code">UNKNOWN</code>? As we told earlier, |
| <code class="inline-code">java.lang</code> and <code class="inline-code">java.util</code> |
| classes are usually converted automatically into |
| <code class="inline-code">TemplateModel</code> implementations, be so called |
| object wrappers. If the object wrapper faces a |
| <code class="inline-code">java.util.Date</code>, that is not an instance of a |
| <code class="inline-code">java.sql</code> date class, it can't decide what the |
| "database style type" is, so it uses <code class="inline-code">UNKNOWN</code>. |
| Later, if the template has to use this variable, and the "database |
| style type" is needed for the operation, it will stop with error. To |
| prevent this, for the problematic variables the template author must |
| help FreeMarker to decide the "database style type", by using the |
| <a href="ref_builtins_date.html#ref_builtin_date_datetype"><code>date</code>, |
| <code>time</code> or <code>datetime</code> |
| built-ins</a>. Note that if you use <code class="inline-code">string</code> |
| built-in with format parameter, as |
| <code class="inline-code">foo?string("MM/dd/yyyy")</code>, then FreeMarker don't |
| need to know the "database style type".</p> |
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