SQL Form Field

Limitation

Using this generic form field type forces you to write SQL in an XML file and is rather limited. For more flexibility, consider creating your own, specific form field type by subclassing the Joomla\CMS\Form\FormField class.

The sql form field type provides a drop down list of entries obtained by running a query on the Joomla database. If the field has a value saved, this value is selected when the page is first loaded. If not, the default value (if any) is selected.

• type (mandatory) must be sql.
• name (mandatory) is the unique name of the field. This must match the name of the query results column that contains the values that will be shown to the user in the drop-down list, unless a different name is specified in the value_field attribute.
• label (mandatory) (translatable) is the field html label.
• query (mandatory if not using the sql_* attributes) is the SQL query which will provide the data for the drop-down list. The query must return two columns; one called 'value' (unless overridden by the key_field attribute) which will hold the values of the list items; the other called the same as the value of the name attribute (unless overridden by the value_field attribute) containing the text to be shown in the drop-down list.
• default (optional) is the default value. This is the value of the 'value' column, unless overridden by the key_field attribute.
• description (optional) (translatable) is the field description.
• multiple (optional) turns the field into a multi-selector. Use multiple="multiple".
• key_field (optional) is the name of the column that will contain values for the parameter. If omitted then the column called 'value' will be used, if it exists.
• value_field (optional) is the name of the column that will contain values to be shown to the user in the drop-down list. If omitted then the column with the same name as the name attribute will be used, if it exists.
• translate (optional) will translate the output of the value_field if set to true. It defaults to false.
• header (optional) (translatable) will add an entry, with an empty value, at the top of the list of options. This is usually used to add a "- Select something -" entry to the list. See the examples for an alternative way of achieving this.
• sql_select (mandatory if not using the query attribute) is the SELECT clause of the SQL statement. Only one such clause is permitted.
• sql_from (mandatory if not using the query attribute) is the FROM clause of the SQL statement.
• sql_join (optional) is the LEFT JOIN clause of the SQL statement. Only one such clause is permitted.
• sql_where (optional) is the WHERE clause of the SQL statement. Only one such clause is permitted.
• sql_group (optional) is the GROUP BY clause of the SQL statement.
• sql_order (optional) is the ORDER BY clause of the SQL statement.
• sql_filter (optional) filters the list by the value of another field. A field name or a comma-separated list of field names can be given. The field names must correspond to column names in the database table being queried. See the examples for further explanation.
• sql_default_{FIELD_NAME} (optional) is the default value used by the sql_filter attribute when the value of the {FIELD_NAME} filter has not been set. See the examples for further explanation.

Implemented by: libraries/src/Form/Field/SqlField.php

Example XML parameter definition

<field
  name="title"
  type="sql"
  default="10"
  label="Select an article"
  query="SELECT id AS value, title AS text FROM #__content"
/>

Notice that an AS clause has been used in this example because the jos_content table does not have a column called 'value'. In fact very few tables in the Joomla database have a column called 'value'.

Alternatively, you can use a key_field attribute to define the column to be used instead of 'value':

<field
  name="title"
  type="sql"
  default="10"
  label="Select an article"
  query="SELECT id, title FROM #__content"
  key_field="id"
/>

This will give identical results to the previous example.

Both column names may need to be aliased. For example, suppose you want your field to be called 'myfield' instead of 'title' in the previous example. Then you can do this:

<field
  name="myfield"
  type="sql"
  default="10"
  label="Select an article"
  query="SELECT id AS value, title AS myfield FROM #__content"
/>

Or alternatively:

<field
  name="myfield"
  type="sql"
  default="10"
  label="Select an article"
  query="SELECT id, title FROM #__content"
  key_field="id"
  value_field="title"
/>

You can also assemble or calculate fields in the SQL statement. For example, suppose you wanted to append the created date/time of each article to the article title in the list. Then you could use this SQL statement:

SELECT
    id,
    concat( title, ' (', created, ')') AS title
FROM
    #__content

You can also specify a static option in the XML using

tag. Please look at the following example.

<field
  name="myfield"
  type="sql"
  default="10"
  label="Select an article"
  query="SELECT id, title FROM #__content"
  key_field="id"
  value_field="title"
  required="true"
>
  <option value="">Please select your option</option>
</field>

Alternatively, you can achieve the same result using the header attribute as follows:

<field
  name="myfield"
  type="sql"
  default="10"
  label="Select an article"
  query="SELECT id, title FROM #__content"
  key_field="id"
  value_field="title"
  required="true"
  header="Please select your option"
/>

Alternative query syntax

Starting with Joomla 3.5, an alternative to the query attribute allows some additional features. These features are not available if the query attribute is present. For example, this field definition:

<field
  name="example_group"
  type="sql"
  label="COM_EXAMPLE_GROUP"
  query="SELECT e.* FROM #__example AS e GROUP BY name ORDER e.id ASC"
  key_field="id"
  value_field="name"
/>

can be expressed as:

<field
  name="example_group"
  type="sql"
  label="COM_EXAMPLE_GROUP"
  sql_select="e.*"
  sql_from="#__example AS e"
  sql_group="name"
  sql_order="e.id ASC"
  key_field="id"
  value_field="name"
/>

Linked Fields as Filters

tip

The description below is quite complex and you may find it helpful to install the example sqlfield component and use it to help you in your understanding.

One advantage to using the alternative syntax above is that it allows the use of linked fields as filters. For example, suppose you have a form containing two select lists, one called groups and the other called subgroups. The groups field is straightforward:

<field 
  name="groups"
  type="sql"
  label="COM_EXAMPLE_GROUPS"
  sql_select="e.*"
  sql_from="#__example_groups AS e"
  sql_group="name"
  sql_order="e.id ASC"
  key_field="id"
  value_field="name"
/>

but the subgroups field includes an sql_filter attribute which refers to the groups field by name:

<field 
  name="subgroups"
  type="sql"
  label="COM_EXAMPLE_SUBGROUPS"
  sql_select="e.*"
  sql_from="#__example_subgroups AS e"
  sql_group="name"
  sql_order="e.id ASC"
  sql_filter="groups"
  key_field="id"
  value_field="name"
  context="sqlfield"
/>

Then if the groups field has the value 99, the following SQL statement will be executed for the subgroups field:

SELECT e.*
FROM
    jos_example_subgroups AS e
WHERE
    `groups` = 99
GROUP BY `name`
ORDER BY e.id ASC

To filter on multiple fields, you can use a comma-separated list of filter names in the sql_filter clause. For example, if there is a filter called groups with the value 99 and a filter called categories with the value 12, then

sql_filter="groups,categories"

will produce the SQL WHERE clause:

WHERE 
    `groups` = 99 
  AND
    `categories` = 12

The context=... attribute is necessary and is described below.

You can also define a default value for any filter that might not have a value when the field is evaluated by adding sql_default_{FIELD_NAME} attributes. For example, suppose that the default value for the groups filter is 0 and the default value for the categories filter is 0, then this definition:

<field 
  name="subgroups"
  type="sql"
  label="COM_EXAMPLE_SUBGROUPS"
  sql_select="e.*"
  sql_from="#__example_subgroups AS e"
  sql_group="name"
  sql_order="e.id ASC"
  sql_filter="groups,categories"
  sql_default_groups="0"
  sql_default_categories="1"
  key_field="id"
  value_field="name"
/>

will produce this SQL statement when initially evaluated with no filters:

SELECT
    e.*
FROM
    jos_example_subgroups AS e
WHERE
    `groups` = 0
  AND
    `categories` = 1
GROUP BY `name`
ORDER BY e.id ASC

Note: The SQL statements will need to be correct for the type and version of the underlying database that Joomla is running on. This will most likely be a version of MySQL, but it could be something else. There is no capability to query databases other than the one Joomla itself is running on.

Note: As shown in these examples, the database prefix (often jos) should be entered in the form #__ (hash-underscore-underscore). It will automatically be replaced by the actual database prefix used by Joomla.

Linked Fields - additional implementation details

It is important to understand what this feature does support and what it doesn't support.

Also, you need to implementation additional code to make the feature work as expected.

Let's take the example where

• the linked filter field is a category field,
• the SQL field is an HTML Select field which shows the titles of articles whose category is selected in the category field.

You want to allow the user to select the category, and then be shown the titles of articles with that category, so that he/she can then select the article.

However, whenever the user selects or changes the category, the code doesn't automatically update the set of titles in the sql field. (There's no Ajax request operating behind the scenes). This update functionality is not part of the supported functionality.

That said, you can implement the functionality to update the titles by following the approach below.

To update the sql field you need to reload the form by

1. sending the current form data to the server (by submitting the form in your javascript code),
2. redisplaying the form via your View class and tmpl file

When you redisplay the form you inject the current form field values into the Form structure. The SQL field will then pick up the key value(s) from the Form structure, and perform the SQL query using these new values, in order to set the new options for the SQL HTML Select field.

To send the form data, implement an onchange javascript listener against the category field, for example, by setting in the XML the file attribute

  onchange="categoryReload(this)"

then implement the javascript categoryReload function:

reload.js

function categoryReload(element) {
    document.body.appendChild(document.createElement('joomla-core-loader'));
    Joomla.submitform(`sqlfield.reload`, element.form, false);
}

This first loads the Joomla spinning logo (which will disappear when the form is re-presented). To call this you need to specify "webcomponent.core-loader" as a dependency in your component's joomla.asset.json file.

Then the form is submitted with

• a task parameter set to 'sqlfield.reload' - change the string 'sqlfield' to your own component Controller name
• the third parameter set to false means that it won't perform field validation before sending the HTTP POST

This POST request will be routed to your SqlfieldController::reload() method.

So you need to include in your SqlfieldController::reload() method something like:

SqlfieldController.php

public function reload($key = null, $urlVar = null)
{
    $this->checkToken();

    $app   = Factory::getApplication();

    $data  = $this->input->post->get('jform', array(), 'array');

    // This is the usual call to set the state for preserving the form data entered by the user
    $app->setUserState('com_sqlfield.example', $data);

    // Then redisplay the form
}

To redisplay the form you can either send the form as an HTTP response to the HTTP POST request:

SqlfieldController.php

    $model = $this->getModel('sqlfield');
    $view = $this->getView('sqlfield', 'html');
    $view->setModel($model, true);
    
    $view->display();

or use the Post/Request/Get pattern to redirect to the DisplayController.

(The example component below uses the first approach).

Example Component

You can download this com_sqlfield component as an example to follow.

Go onto your Joomla instance back-end, display the article categories and find the id of your Uncategorised category.

If it's not 2 then edit the com_sqlfield site/forms/example_form.xml and set the sql_default_catid to whatever id it is.

Install the com_sqlfield component and run the form by navigating to your Joomla instance's site page index.php?option=com_sqlfield

The component will display an HTML select field with the article categories available on your instance, and in the next field, the titles of the articles associated with the selected category.

If you select a different category then the component will send the form data to the server in an HTTP POST request, with the task parameter set to "sqlfield.reload" which will cause the SqlfieldController::reload() function to be called. This function stores the existing form values in the user state, and arranges for the form to be redisplayed.

When the component redisplays the form it injects the existing form values into the Joomla Form structure, (so that when the form is redisplayed the user sees the values he/she previously entered). The SQL Field can then obtain the category from this Form structure, and perform a SQL query to obtain the articles associated with the selected category. These article ids and titles will be set as options in the field, and will be shown when the form is re-presented.

When you press Select then the selected category and article will be sent to the server in the HTTP POST request, together with the task set to "sqlfield.submit", and the component code then displays the selected ids in the associated HTTP POST response.

See also

• Secure DB Queries