📄 selval.htm
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<title>SelVal</title>
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vlink="#551A8B" alink="#FF0000">
<p><font size="6" face="Bookman Old Style"><em><strong><u>dtl</u></strong></em></font></p>
<p><img src="stat.gif" width="6" height="6"> <!--end header--> <br>
</p>
<h1>SelVal</h1>
<table border="0" cellpadding="0" cellspacing="0" width="100%">
<tr>
<td><img src="functors.gif" width="194" height="38"></td>
<td align="right"><img src="concept.gif" width="194"
height="39"></td>
</tr>
<tr>
<td valign="top"><b>Category</b>: functors</td>
<td align="right" valign="top"><b>Component type</b>:
concept</td>
</tr>
</table>
<h3>Description</h3>
<p><font size="2" face="Courier New">SelVal</font> is a function object
(this can be a wrapped function pointer if you use
<a href="cb_ptr_fun.htm"> <font size="2" face="Courier New">cb_ptr_fun_w_ret()</font></a>)
that is called to to validate a user defined <font size="2"
face="Courier New">DataObj</font> as it is read from the database.
The function returns <font size="2" face="Courier New">true</font>
if the <font size="2" face="Courier New">DataObj </font>contains
a valid set of fields, <font size="2" face="Courier New">false</font>
otherwise. <font size="2" face="Courier New">SelVal </font>is
called on each record read from a database via either <a
href="DBView.htm"><font size="2" face="Courier New">DBView</font></a><font
size="2" face="Courier New"> </font>or <a
href="IndexedDBView.htm"><font size="2"
face="Courier New">IndexedDBView</font></a><font size="2"
face="Courier New">. </font>The default behavior of a <font
size="2" face="Courier New">SelVal </font>can be found in the<font
size="2" face="Courier New"> DefaultSelValidate<DataObj></font>
template. This particular functor returns<font size="2"
face="Courier New"> true</font> if all of the fields read into
the <font size="2" face="Courier New">BoundIOs </font>have a
value (that is, all fetched columns are non-NULL, tested using <font
size="2" face="Courier New">BoundIO::IsNull()</font>), otherwise
it returns <font size="2" face="Courier New">false</font>.
Through the use of template specialization, you can customize the
default behavior for this functor by writing your own <font
size="2" face="Courier New">DefaultSelValidate<DataObj> </font>for
that class of <font size="2" face="Courier New">DataObj's.</font></p>
<h3>Refinement of</h3>
<p>None.</p>
<h3>Associated types</h3>
<p><a href="BoundIO.htm"><font size="2" face="Courier New">BoundIOs</font></a><font
size="2" face="Courier New">.</font></p>
<h3>Example 1:</h3>
<pre><code><span class="codeComment">//Default SelVal function to make sure fields in a row selected from the database are valid
// Default select validation behavior ... data is valid if and only if
// there are no columns which are null.
// If there are other checks you wish to make, put them in
// your own SelVal functor.
// You can also specialize this template if you wish to have different default behavior
// for your data class.</span>
template<class DataObj> class DefaultSelValidate {
public:
bool operator()(BoundIOs &boundIOs,DataObj &rowbuf)
{
for (BoundIOs::iterator b_it = boundIOs.begin();
b_it != boundIOs.end(); b_it++)
{
BoundIO &boundIO = (*b_it).second;
if (boundIO.IsColumn() && boundIO.IsNull())
return false; <span class="codeComment">// found null column ... data is invalid</span>
}
return true; <span class="codeComment">// no nulls found ... data is OK</span>
}
};
</code></pre>
<h3>Example 2:</h3>
<pre><code><span class="codeComment">// Assign valid defaults for null values</span>
class Example
{
public: <span class="codeComment">// tablename.columnname:</span>
int exampleInt; <span class="codeComment">// DB_EXAMPLE.INT_VALUE</span>
string exampleStr; <span class="codeComment">// DB_EXAMPLE.STRING_VALUE</span>
double exampleDouble; <span class="codeComment">// DB_EXAMPLE.DOUBLE_VALUE</span>
long exampleLong; <span class="codeComment">// DB_EXAMPLE.EXAMPLE_LONG</span>
TIMESTAMP_STRUCT exampleDate; <span class="codeComment">// DB_EXAMPLE.EXAMPLE_DATE</span>
};
<span class="codeComment">// Validation behavior, assign default values for NULL fields</span>
template<> class dtl::DefaultSelValidate<Example>
{
public:
bool operator()(BoundIOs &boundIOs, Example &rowbuf) {
if (boundIOs["INT_VALUE"].IsNull()) {
rowbuf.exampleInt = 0;
}
if (boundIOs["STRING_VALUE"].IsNull()) {
rowbuf.exampleStr = "";
}
if (boundIOs["DOUBLE_VALUE"].IsNull()) {
rowbuf.exampleDouble = 0;
}
if (boundIOs["EXAMPLE_LONG"].IsNull()) {
rowbuf.exampleLong = 0;
}
if (boundIOs["EXAMPLE_DATE"].IsNull()) {
const TIMESTAMP_STRUCT defaultDate = {2000, 1, 1, 0, 0, 0, 0};
rowbuf.exampleDate = defaultDate;
}
<span class="codeComment">// Now check that values are in acceptable range
// Return false/failure if values out of range</span>
if (rowbuf.exampleDouble > 100)
return false;
return true; // data is OK
}
};</code></pre>
<p> </p>
<p> </p>
<h3>Notation</h3>
<table border="0">
<tr>
<td valign="top"><tt>X</tt> </td>
<td valign="top">A type that is a model of <font size="2"
face="Courier New">SelVal</font></td>
</tr>
<tr>
<td valign="top"><tt>a</tt> </td>
<td valign="top">Object of type <tt>X</tt> </td>
</tr>
</table>
<h3>Expression semantics</h3>
<table border="1">
<tr>
<th>Name </th>
<th>Expression </th>
<th>Precondition </th>
<th>Semantics </th>
<th>Postcondition </th>
</tr>
<tr>
<td valign="top">Default constructor </td>
<td valign="top"><pre>X a()</pre>
</td>
<td valign="top"> </td>
<td valign="top">Construct the function object.</td>
<td valign="top"> </td>
</tr>
<tr>
<td valign="top">Copy constructor </td>
<td valign="top"><pre>X a(constX &b)</pre>
</td>
<td valign="top"> </td>
<td valign="top">Copy construct the<font size="2"
face="Courier New"> SelVal</font>.</td>
<td valign="top"> </td>
</tr>
<tr>
<td valign="top">Assignment operator</td>
<td valign="top"><pre>X& operator=(const X&b)</pre>
</td>
<td valign="top"> </td>
<td valign="top">Assignment copy</td>
<td valign="top"> </td>
</tr>
<tr>
<td valign="top">Validate operator</td>
<td valign="top"><pre>void operator()(BoundIOs &boundIOs, DataObj &rowbuf))</pre>
</td>
<td valign="top"> </td>
<td valign="top">This operator takes a <font size="2"
face="Courier New">BoundIOs</font> object and a reference
to a <font size="2" face="Courier New">rowbuf</font>
holding a user defined data object. The job of the
function is to validate the user defined data object and/or
make any default assignments in the data object in the
case of <font size="2" face="Courier New">NULL</font>
fields. On exit, the function should return <font
size="2" face="Courier New">true</font> if it was able to
validate the data object, <font size="2"
face="Courier New">false </font>otherwise.</td>
<td valign="top">The fields in <font size="2"
face="Courier New">DataObj </font>that are bound to query
parameters should be initialized with valid values if the
function returns <font size="2" face="Courier New">true</font>.</td>
</tr>
</table>
<h3>Notes</h3>
<p>None.</p>
<h3>See also</h3>
<p><a href="BoundIO.htm"><font size="2" face="Courier New">BoundIOs</font></a><font
size="2" face="Courier New">, </font><a href="BCA.htm"><font
size="2" face="Courier New">BCA</font></a><font size="2"
face="Courier New">, </font><a href="BPA.htm"><font size="2"
face="Courier New">BPA</font></a><font size="2"
face="Courier New">, </font><a href="DBView.htm"><font
size="2" face="Courier New">DBView</font></a><font size="2"
face="Courier New">, </font><a
href="IndexedDBView.htm"><font size="2"
face="Courier New">IndexedDBView</font></a><a
href="IndexedDBView.htm"><font size="2"><!--start footer--></font></a></p>
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