Файл: CodeIgniter-3.0.3/user_guide/database/metadata.html
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<div class="section" id="database-metadata">
<h1>Database Metadata<a class="headerlink" href="#database-metadata" title="Permalink to this headline">¶</a></h1>
<div class="section" id="table-metadata">
<h2>Table MetaData<a class="headerlink" href="#table-metadata" title="Permalink to this headline">¶</a></h2>
<p>These functions let you fetch table information.</p>
<div class="section" id="list-the-tables-in-your-database">
<h3>List the Tables in Your Database<a class="headerlink" href="#list-the-tables-in-your-database" title="Permalink to this headline">¶</a></h3>
<p><strong>$this->db->list_tables();</strong></p>
<p>Returns an array containing the names of all the tables in the database
you are currently connected to. Example:</p>
<div class="highlight-ci"><div class="highlight"><pre><span class="nv">$tables</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">list_tables</span><span class="p">();</span>
<span class="k">foreach</span> <span class="p">(</span><span class="nv">$tables</span> <span class="k">as</span> <span class="nv">$table</span><span class="p">)</span>
<span class="p">{</span>
<span class="k">echo</span> <span class="nv">$table</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
</div>
<div class="section" id="determine-if-a-table-exists">
<h3>Determine If a Table Exists<a class="headerlink" href="#determine-if-a-table-exists" title="Permalink to this headline">¶</a></h3>
<p><strong>$this->db->table_exists();</strong></p>
<p>Sometimes it’s helpful to know whether a particular table exists before
running an operation on it. Returns a boolean TRUE/FALSE. Usage example:</p>
<div class="highlight-ci"><div class="highlight"><pre><span class="k">if</span> <span class="p">(</span><span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">table_exists</span><span class="p">(</span><span class="s1">'table_name'</span><span class="p">))</span>
<span class="p">{</span>
<span class="c1">// some code...</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Replace <em>table_name</em> with the name of the table you are looking for.</p>
</div>
</div>
</div>
<div class="section" id="field-metadata">
<h2>Field MetaData<a class="headerlink" href="#field-metadata" title="Permalink to this headline">¶</a></h2>
<div class="section" id="list-the-fields-in-a-table">
<h3>List the Fields in a Table<a class="headerlink" href="#list-the-fields-in-a-table" title="Permalink to this headline">¶</a></h3>
<p><strong>$this->db->list_fields()</strong></p>
<p>Returns an array containing the field names. This query can be called
two ways:</p>
<p>1. You can supply the table name and call it from the $this->db->
object:</p>
<div class="highlight-ci"><div class="highlight"><pre><span class="nv">$fields</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">list_fields</span><span class="p">(</span><span class="s1">'table_name'</span><span class="p">);</span>
<span class="k">foreach</span> <span class="p">(</span><span class="nv">$fields</span> <span class="k">as</span> <span class="nv">$field</span><span class="p">)</span>
<span class="p">{</span>
<span class="k">echo</span> <span class="nv">$field</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
<p>2. You can gather the field names associated with any query you run by
calling the function from your query result object:</p>
<div class="highlight-ci"><div class="highlight"><pre><span class="nv">$query</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">query</span><span class="p">(</span><span class="s1">'SELECT * FROM some_table'</span><span class="p">);</span>
<span class="k">foreach</span> <span class="p">(</span><span class="nv">$query</span><span class="o">-></span><span class="na">list_fields</span><span class="p">()</span> <span class="k">as</span> <span class="nv">$field</span><span class="p">)</span>
<span class="p">{</span>
<span class="k">echo</span> <span class="nv">$field</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
</div>
<div class="section" id="determine-if-a-field-is-present-in-a-table">
<h3>Determine If a Field is Present in a Table<a class="headerlink" href="#determine-if-a-field-is-present-in-a-table" title="Permalink to this headline">¶</a></h3>
<p><strong>$this->db->field_exists()</strong></p>
<p>Sometimes it’s helpful to know whether a particular field exists before
performing an action. Returns a boolean TRUE/FALSE. Usage example:</p>
<div class="highlight-ci"><div class="highlight"><pre><span class="k">if</span> <span class="p">(</span><span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">field_exists</span><span class="p">(</span><span class="s1">'field_name'</span><span class="p">,</span> <span class="s1">'table_name'</span><span class="p">))</span>
<span class="p">{</span>
<span class="c1">// some code...</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Replace <em>field_name</em> with the name of the column you are looking
for, and replace <em>table_name</em> with the name of the table you are
looking for.</p>
</div>
</div>
<div class="section" id="retrieve-field-metadata">
<h3>Retrieve Field Metadata<a class="headerlink" href="#retrieve-field-metadata" title="Permalink to this headline">¶</a></h3>
<p><strong>$this->db->field_data()</strong></p>
<p>Returns an array of objects containing field information.</p>
<p>Sometimes it’s helpful to gather the field names or other metadata, like
the column type, max length, etc.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Not all databases provide meta-data.</p>
</div>
<p>Usage example:</p>
<div class="highlight-ci"><div class="highlight"><pre><span class="nv">$fields</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">field_data</span><span class="p">(</span><span class="s1">'table_name'</span><span class="p">);</span>
<span class="k">foreach</span> <span class="p">(</span><span class="nv">$fields</span> <span class="k">as</span> <span class="nv">$field</span><span class="p">)</span>
<span class="p">{</span>
<span class="k">echo</span> <span class="nv">$field</span><span class="o">-></span><span class="na">name</span><span class="p">;</span>
<span class="k">echo</span> <span class="nv">$field</span><span class="o">-></span><span class="na">type</span><span class="p">;</span>
<span class="k">echo</span> <span class="nv">$field</span><span class="o">-></span><span class="na">max_length</span><span class="p">;</span>
<span class="k">echo</span> <span class="nv">$field</span><span class="o">-></span><span class="na">primary_key</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
<p>If you have run a query already you can use the result object instead of
supplying the table name:</p>
<div class="highlight-ci"><div class="highlight"><pre><span class="nv">$query</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">query</span><span class="p">(</span><span class="s2">"YOUR QUERY"</span><span class="p">);</span>
<span class="nv">$fields</span> <span class="o">=</span> <span class="nv">$query</span><span class="o">-></span><span class="na">field_data</span><span class="p">();</span>
</pre></div>
</div>
<p>The following data is available from this function if supported by your
database:</p>
<ul class="simple">
<li>name - column name</li>
<li>max_length - maximum length of the column</li>
<li>primary_key - 1 if the column is a primary key</li>
<li>type - the type of the column</li>
</ul>
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