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
- class views_object
Expanded class hierarchy of views_handler_relationship_groupwise_max
Related topics
File
- core/
modules/ views/ handlers/ views_handler_relationship_groupwise_max.inc, line 55 - Relationship for groupwise maximum handler.
Members
Name | Modifiers | Type | Description |
---|---|---|---|
views_object:: |
function | ||
views_object:: |
function | ||
views_handler:: |
function | Called just prior to query(), this lets a handler set up any relationship it needs. | |
views_handler_relationship_groupwise_max:: |
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:: |
|
views_handler:: |
function | Check whether current user has access to this handler. | |
views_handler:: |
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_relationship_groupwise_max:: |
function |
Defines default values for options. Overrides views_handler_relationship:: |
|
views_handler:: |
function | Determine if a handler can be exposed. | |
views_handler:: |
function | Determine if the argument needs a style plugin. | |
views_handler:: |
function | Determine if the handler is considered 'broken', meaning it's a a placeholder used when a handler can't be found. | |
views_handler:: |
function | Determine if this item is 'exposed', meaning it provides form elements to let users modify the view. | |
views_handler:: |
function | Ensure the main table for this handler is in the query. This is used a lot. | |
views_handler_relationship_groupwise_max:: |
function |
Extends the relationship's basic options, allowing the user to pick
a sort and an order for it. Overrides views_handler_relationship:: |
|
views_handler:: |
function | Form for exposed handler options. | |
views_handler_relationship_groupwise_max:: |
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:: |
function | Get information about the exposed form for the form renderer. | |
views_handler:: |
function | Get the join object that should be used for this handler. | |
views_handler_relationship:: |
function | Get this field's label. | |
views_handler_relationship_groupwise_max:: |
function | Helper function to create a pseudo view. | |
views_handler_relationship_groupwise_max:: |
function | Helper function to namespace query pieces. | |
views_handler:: |
function | If a handler has 'extra options' it will get a little settings widget and another form called extra_options. | |
views_handler:: |
function | If set to remember exposed input in the session, store it there. | |
views_handler_relationship:: |
function |
Init handler to let relationships live on tables other than
the table they operate on. Overrides views_handler:: |
|
views_object:: |
function | Let the handler know what its full definition is. | |
views_handler:: |
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:: |
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:: |
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:: |
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:: |
function | Provide a form for aggregation settings. | |
views_handler:: |
function | Provide a form for setting options. | |
views_handler:: |
function | Provide defaults for the handler. | |
views_handler:: |
function | Provide text for the administrative summary | |
views_handler:: |
function | Provides a unique placeholders for handlers. | |
views_handler_relationship_groupwise_max:: |
function | Recursive helper to add a namespace to conditions. | |
views_handler:: |
function | Render our chunk of the exposed handler form when selecting | |
views_handler:: |
function | Return a string representing this handler's name in the UI. | |
views_handler:: |
function | Returns TRUE if the exposed filter works like a grouped filter. | |
views_handler:: |
function | Run after the view is executed, before the result is cached. | |
views_handler:: |
function | Run before the view is built. | |
views_handler:: |
function | Sanitize the value for output. | |
views_object:: |
function | Set default options on this object. Called by the constructor in a complex chain to deal with backward compatibility. | |
views_object:: |
function | Set default options. For backward compatibility, it sends the options array; this is a feature that will likely disappear at some point. | |
views_handler:: |
function | Set new exposed option defaults when exposed setting is flipped on. | |
views_handler:: |
function | Shortcut to display the expose/hide button. | |
views_handler:: |
function | Shortcut to display the exposed options form. | |
views_handler:: |
function | Shortcut to get a handler's raw field value. | |
views_handler:: |
function | Submit the exposed handler form | |
views_handler:: |
function | Take input from exposed handlers and assign to this handler, if necessary. | |
views_handler:: |
public | property | The alias of the table of this handler which is used in the query. |
views_handler:: |
public | property | The Views name of the table on which this handler effects. |
views_handler:: |
function | Transform a string by a certain method. | |
views_object:: |
public | function | Unpack a single option definition. |
views_object:: |
function | Unpack options over our existing defaults, drilling down into arrays so that defaults don't get totally blown away. | |
views_object:: |
public | function | Unpacks each handler to store translatable texts. |
views_handler:: |
function | Validate the exposed handler form | |
views_handler:: |
function | Validate the options form. | |
views_handler:: |
function | Validate the options form. | |
views_handler:: |
function | Validate the options form. | |
views_handler:: |
function | Validates the handler against the complete View. | |
views_object:: |
function | Views handlers use a special construct function so that we can more easily construct them with variable arguments. | |
views_handler_relationship_groupwise_max:: |
function | When the form is submitted, take sure to clear the subquery string cache. | |
views_handler_relationship:: |
function |
You can't groupby a relationship. Overrides views_handler:: |