Relationship handler that allows a groupwise maximum of the linked in table. For a definition, see: http://dev.mysql.com/doc/refman/5.0/en/example-maximum-column-group-row.... In lay terms, instead of joining to get all matching records in the linked table, we get only one record, a 'representative record' picked according to a given criteria.

Example: Suppose we have a term view that gives us the terms: Horse, Cat, Aardvark. We wish to show for each term the most recent node of that term. What we want is some kind of relationship from term to node. But a regular relationship will give us all the nodes for each term, giving the view multiple rows per term. What we want is just one representative node per term, the node that is the 'best' in some way: eg, the most recent, the most commented on, the first in alphabetical order.

This handler gives us that kind of relationship from term to node. The method of choosing the 'best' implemented with a sort that the user selects in the relationship settings.

So if we want our term view to show the most commented node for each term, add the relationship and in its options, pick the 'Comment count' sort.

Relationship definition

  • 'outer field': The outer field to substitute into the correlated subquery. This must be the full field name, not the alias. Eg: 'term_data.tid'.
  • 'argument table', 'argument field': These options define a views argument that the subquery must add to itself to filter by the main view. Example: the main view shows terms, this handler is being used to get to the nodes base table. Your argument must be 'term_node', 'tid', as this is the argument that should be added to a node view to filter on terms.

A note on performance: This relationship uses a correlated subquery, which is expensive. Subsequent versions of this handler could also implement the alternative way of doing this, with a join -- though this looks like it could be pretty messy to implement. This is also an expensive method, so providing both methods and allowing the user to choose which one works fastest for their data might be the best way. If your use of this relationship handler is likely to result in large data sets, you might want to consider storing statistics in a separate table, in the same way as node_comment_statistics.

Hierarchy

Expanded class hierarchy of views_handler_relationship_groupwise_max

Related topics

File

core/modules/views/handlers/views_handler_relationship_groupwise_max.inc, line 56
Relationship for groupwise maximum handler.

Members

Contains filters are case sensitive
Namesort descending Modifiers Type Description
views_handler::$table public property The Views name of the table on which this handler effects.
views_handler::$table_alias public property The alias of the table of this handler which is used in the query.
views_handler::accept_exposed_input function Take input from exposed handlers and assign to this handler, if necessary.
views_handler::access function Check whether current user has access to this handler.
views_handler::admin_summary function Provide text for the administrative summary
views_handler::broken function Determine if the handler is considered 'broken', meaning it's a a placeholder used when a handler can't be found.
views_handler::can_expose function Determine if a handler can be exposed.
views_handler::case_transform function Transform a string by a certain method.
views_handler::ensure_my_table function Ensure the main table for this handler is in the query. This is used a lot.
views_handler::exposed_form function Render our chunk of the exposed handler form when selecting
views_handler::exposed_info function Get information about the exposed form for the form renderer.
views_handler::exposed_submit function Submit the exposed handler form
views_handler::exposed_validate function Validate the exposed handler form
views_handler::expose_form function Form for exposed handler options.
views_handler::expose_options function Set new exposed option defaults when exposed setting is flipped on.
views_handler::expose_submit function Perform any necessary changes to the form exposes prior to storage. There is no need for this function to actually store the data.
views_handler::expose_validate function Validate the options form.
views_handler::extra_options function Provide defaults for the handler.
views_handler::extra_options_form function Provide a form for setting options.
views_handler::extra_options_submit function Perform any necessary changes to the form values prior to storage. There is no need for this function to actually store the data.
views_handler::extra_options_validate function Validate the options form.
views_handler::get_field function Shortcut to get a handler's raw field value.
views_handler::get_join function Get the join object that should be used for this handler.
views_handler::groupby_form function Provide a form for aggregation settings.
views_handler::groupby_form_submit function Perform any necessary changes to the form values prior to storage. There is no need for this function to actually store the data.
views_handler::has_extra_options function If a handler has 'extra options' it will get a little settings widget and another form called extra_options.
views_handler::is_a_group function Returns TRUE if the exposed filter works like a grouped filter.
views_handler::is_exposed function Determine if this item is 'exposed', meaning it provides form elements to let users modify the view.
views_handler::multiple_exposed_input function Define if the exposed input has to be submitted multiple times. This is TRUE when exposed filters grouped are using checkboxes as widgets.
views_handler::needs_style_plugin function Determine if the argument needs a style plugin.
views_handler::options_submit function Perform any necessary changes to the form values prior to storage. There is no need for this function to actually store the data.
views_handler::options_validate function Validate the options form.
views_handler::placeholder function Provides a unique placeholders for handlers.
views_handler::post_execute function Run after the view is executed, before the result is cached.
views_handler::pre_query function Run before the view is built.
views_handler::sanitize_value function Sanitize the value for output.
views_handler::set_relationship function Called just prior to query(), this lets a handler set up any relationship it needs.
views_handler::show_expose_button function Shortcut to display the expose/hide button.
views_handler::show_expose_form function Shortcut to display the exposed options form.
views_handler::store_exposed_input function If set to remember exposed input in the session, store it there.
views_handler::ui_name function Return a string representing this handler's name in the UI.
views_handler::validate function Validates the handler against the complete View.
views_handler_relationship::init function Init handler to let relationships live on tables other than the table they operate on. Overrides views_handler::init
views_handler_relationship::label function Get this field's label.
views_handler_relationship::use_group_by function You can't groupby a relationship. Overrides views_handler::use_group_by
views_handler_relationship_groupwise_max::alter_subquery_condition function Recursive helper to add a namespace to conditions.
views_handler_relationship_groupwise_max::condition_namespace function Helper function to namespace query pieces.
views_handler_relationship_groupwise_max::get_temporary_view function Helper function to create a pseudo view.
views_handler_relationship_groupwise_max::left_query function Generate a subquery given the user options, as set in the options. These are passed in rather than picked up from the object because we generate the subquery when the options are saved, rather than when the view is run. This saves considerable time.
views_handler_relationship_groupwise_max::options_form function Extends the relationship's basic options, allowing the user to pick a sort and an order for it. Overrides views_handler_relationship::options_form
views_handler_relationship_groupwise_max::options_form_submit function When the form is submitted, take sure to clear the subquery string cache.
views_handler_relationship_groupwise_max::option_definition function Defines default values for options. Overrides views_handler_relationship::option_definition
views_handler_relationship_groupwise_max::query function Called to implement a relationship in a query. This is mostly a copy of our parent's query() except for this bit with the join class. Overrides views_handler_relationship::query
views_object::construct function Views handlers use a special construct function so that we can more easily construct them with variable arguments.
views_object::destroy function
views_object::options Deprecated function Set default options on this object. Called by the constructor in a complex chain to deal with backward compatibility.
views_object::set_default_options function Set default options. For backward compatibility, it sends the options array; this is a feature that will likely disappear at some point.
views_object::set_definition function Let the handler know what its full definition is.
views_object::unpack_options function Unpack options over our existing defaults, drilling down into arrays so that defaults don't get totally blown away.
views_object::unpack_translatable public function Unpack a single option definition.
views_object::unpack_translatables public function Unpacks each handler to store translatable texts.
views_object::_set_option_defaults function