API:Accessing Data

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Getting data out of CollectiveAccess is, for obvious reasons, one of the most commonly performed tasks when writing code. Whether you're writing an import/export script, an application plugin or a web front-end, odds are you'll be doing a lot of getting of data!

In a typical database application you usually just execute SQL queries and directly read field data. Things are a bit more complicated in CollectiveAccess, owing to the extra functionality the application layers upon its relational database. CollectiveAccess supports many features not present in a typical database-driven application, including user defined fields, complex (multi-valued) fields, repeating fields, "media" fields (fields that hold uploaded media, media metadata and derivatives), and historic-scale date range expressions. Moreover, virtually every information item in the database is tagged with a language/locale to provide for multilingual content. Direct queries on the database, unless specially crafted, may return the same content in several languages – leaving you to figure out which is the most appropriate language to use.

Methods of Access

Broadly speaking, there are three methods of accessing data stored in CollectiveAccess:

  1. Using direct SQL queries on the database: You can always get at your data using the standard MySQL database client. You can also use CollectiveAccess' database access library, Db, located in app/lib/core/Db.php. There is nothing wrong with directly interacting with the database – obviously, the underlying CollectiveAccess application libraries do this all the time, and for some tasks this will be the best performing option – but for most tasks direct SQL queries will result in a lot more code and a lot more work. If you perform direct queries you are accessing the raw data store. Some values, dates for example, are stored in specific formats (either Unix-time or CollectiveAccess' own "historic date range" format) that must be parsed prior to display. Attributes (user defined, possibly repeating, fields) are stored in a generic fashion that depending upon field type may require some parsing as well. And media fields must be processed to resolve URL and server paths prior to use. Further all multilingual content must be processed to extract the particular language you require. (It may seem simple to filter on language, but unless your database has full translation of all content – a rare occurrence – you must negotiate languages to find the best match given the user. This is a more complicated task.)
  2. Load a specific row in a specific table using an instance of the table's Model class : all tables in the CollectiveAccess database that you'd need to access directly have corresponding model classes located in app/models. You can access any row in a table by creating an instance of the model and load()'ing the row, either by unique row_id or by one or more field values.
  3. Load a set of rows from a specific table using the search engine: you can use the search engine (via a table-specific subclass such as ObjectSearch or PlaceSearch (located in app/lib/ca/Search) to find and access rows. The engine returns the result set in a subclass of SearchResult (located in app/lib/core/Search). For example, for searches via ObjectSearch on the ca_objects table the result set object will be of class ObjectSearchResult. The result object will provide functionality for getting information out of the search result for display, as well as functionality specific to the type of data being search for. (For example, ObjectSearchResult includes special methods for getting related media for display; the other SearchResult sub-classes don't have these functions because they don't support related media.) The browse engine returns results in a similar manner, with its own classes (eg. ObjectBrowseResult) that inherit from the same parent and implement the same functionality as their search counterparts. In general, whatever you can do with a search result can be done with a browse result too.

In general you should be using the latter two options in your code unless you have good reason to be performing direct database queries

Types of information

CollectiveAccess stores information relating to catalogued items (collections objects, lots and authorities) can be classified into four groups:

  1. Intrinsic fields : these are standard database fields hardcoded into the database and guaranteed to exist in all installations. They do not repeat and do not take field-level language/locale values. An example of a commonly used intrinsic field would be ca_objects.idno, the "object identifier"(aka. accession number) field. Since objects always have an accession number, and the number is non-repeating and locale-less (it's the same regardless of language) idno for objects is implemented as intrinsic.
  2. Labels : these are representative names or titles of catalogued items. Labels take locales/languages and are divided into two types: preferred labels and non-preferred labels. A preferred label is the one "true" title or name of an item – the one you should use when referring to the item – used for display. There can only be one preferred label per item per locale. That is, if you are cataloguing in three languages you can have up to three preferred labels, one in each language. Non-preferred labels are alternative names that can be used to enhance searching or preserve identity. Non-preferred labels can repeat without limit, take locales and optionally take type values which may be employed distinguish valid "alternate" labels from simple search enhancing non-preferred labels.
  3. Attributes : typically the majority of information in a CollectiveAccess database, attributes are values of various types attached to items and structured according to an installation specific schema. The structure and meaning of attributes are defined by metadata element definitions. These definitions can be simple fields (eg. a single text value) or complex values made up of many elements assembled into a hierarchy (sometimes referred to as an "element set" or "compound attribute"; an address with separate fields for street, city, state, postal code, etc. is an example of a complex value). Whether simple or complex, each metadata element definition is bound via type restrictions to any type of item (object, entity, place, etc.) and, optionally, to specific types of item. The binding includes restrictions on how the element repeats (or not) when used with a given type of item. In short: attributes are user defined data elements that may contain many types of structured data, can be single values or collections of many values, can repeat any number of times (or not) and can be tagged with a locale (or not).
  4. Related items : relationships may be established between items. For example, if an object was painted by a person, then the object's record will have a relationship to the entity record for the painter. Relationships are qualified by relationship types; in the previous example the relationship would likely have a type of "artist" or perhaps "painter." The precise set of relationship types will vary from installation to installation, but the set of possible relationships will not. With a few exceptions, all primary item types (objects, object lots, entities, places, occurrences, collections, list items, storage locations, loans and movements) may be interrelated without restriction.

Bundle specifiers

The four types of information described above are collectively referred to as bundles. When using the CollectiveAccess API to access a bundle, a bundle specifier must be used. This is just a fancy-speak for a name. The rules for creating these names are simple. Each bundle specifier is composed of between one and four parts joined together with periods. The first part is always the table name for the item you want to pull data from. The table names for primary item types are:

Item Table name
Objects ca_objects
Object lots ca_object_lots
Entities ca_entities
Places ca_places
Occurrences ca_occurrences
Collections ca_collections
Storage locations ca_storage_locations
Loans ca_loans
Movements ca_movements

The second part is a field name (for intrinsic fields), a metadata element code (for attributes), preferred_labels or nonpreferred_labels. The third part is a sub-element code, when used with complex attributes, or a sub-field name when used with preferred or nonpreferred labels. Complex attributes and labels both have more than a single value associated with them. For example, an entity label contains fields for each piece of a name, including forename, surname, middle name, and title/prefix. The sub-element/sub-field lets you specify which value in the collection you want.

If you are dealing with an item that is part of a hierarchy, you can specify values immediately up or down the hierarchy from the item you are working with by setting the second element to either parent or children. The other elements function the similarly except that they slide down to the third and fourth positions respectively.

Intrinsic fields

The bundle specifier for an intrinsic field is simply the table name + the field name. For example, the specifier for the object identifier (aka "accession number") is ca_objects.idno To get the status value for an entity the specifier in ca_entities.status. You can get a list of fields for the various items by looking at the table definition in the database schema (located in install/inc/schema_mysql.sql).

Labels

There are two formats for preferred label specifiers. The simplest specifier is table name + preferred_labels, which will return the "display" value for the label. For most labels this is the name or title. For entities, which has a more complex label structure than other items, this is the displayname field.

The specifier for a specific label field is table name + preferred_labels + label field name. For example, if you want the surname field of the preferred entity label, you would use ca_entities.preferred_labels.surname

Non preferred labels work similarly, except of course that you use nonpreferred_labels in place of preferred_labels.

Attributes

To form a specifier for a simple single-value attribute, use table name + element code. For complex attributes use table name + the element code of the root (top-of-hierarchy) container + sub-element code. The namespace for element codes is flat, so no matter how deep the hierarchy you need only specify the code of the specific sub-element. You don't have to mimic the hierarchical structure.

For instance, to get the internal_notes attribute from an object, you might use ca_objects.internal_notes. To get the city value from an entity address, where the element code for city is city and the element code for the root container is address', you would use ca_entities.address.city. Naturally, the element codes depend upon how your system is configured.

Related items

When used with the table name of the item at hand, all of the specifier formats described so far fetch values directly attached to that item. That is, if you have an object record and invoke ca_objects.description you will get the value of the description attribute attached to the object record. If you use other table names, CA will automatically traverse relationships and fetch values from related records in the specified table. For example, if you are working with an object record and use the specifier ca_entities.preferred_labels.displayname you'll fetch all of the display names of entities related to the object. Similarly, if you use ca_places.idno you'll obtain a list of place identifiers for places related to the object at hand.

Anything directly attached to the record at hand can also be fetched from related records by varying the table name.

If you wish to get "self relations" - entities related to an entity for example - you must use the related qualifier. For example, to fetch the names of entities related to an entity use the specified ca_entities.related.preferred_labels.displayname. If you omit the related in this case you'd get the name of the entity at hand rather than the related ones.

You can include the related qualifier in any relationship specifier but it is only required when traversing self-relations.

Traversing hierarchical items

Many types of items can be assembled into hierarchies. Some, notably places, list items and storage locations, are almost always hierarchical. Others, including objects and collections, can be optionally assembled into hierarchies as required. You can specify values from records immediately above or below the one at hand in the hierarchy by using parent and children values as the second element of your specifier. The other elements continue to function normally when using parent and children – they just apply to records elsewhere in the hierarchy.

For example, for a given place you can fetch the name of the parent using ca_places.parent.preferred_labels.name. You can fetch the plural names of children of a list item using ca_list_items.children.preferred_labels.name_plural

If you simply need the entire hierarchical path to the item at hand, use the "hierarchy" specifier. For example, getting ca_places.hierarchy will return the name of the place at hand as well as the names of some or all of its hierarchical parents, in order. By default the value returned for each item in the hierarchy is the label display field (eg. name for ca_objects, ca_places and several others; displayname for ca_entities), but you can also specify other label fields if required. For example ca_objects.hierarchy.name_sort will return the hierarchy using sortable name fields for the objects. There are several special options available when getting hierarchies:

  1. direction determines how the hierarchy is sorted. "ASC" (the default) will return the hierarchy with root first. "DESC" will return the hierarchy with the lowest child element first.
  2. hierarchicalDelimiter sets what characters are displayed between items in the hierarchy list, when you get the list as a string. If this is not set then the value of the delimiter option is used.
  3. top, if set to a non-zero number, limits the returned hierarchy to the first X items root down.
  4. bottom, if set to a non-zero number, limits the returned hierarchy to the last X items from the lowest child up.
  5. removeFirstItems, if set to a non-zero number, will cause the removal of the specified number of items off of the hierarchy, starting with the root, before sorting or any other processing is performed.

If the returnAsArray option is set then the hierarchy is returned as an array of items. The returnAllLocales is not supported for the hierarchy specifier.

Getting data from model instances and search results

In the discussion above we refer to the "item at hand." In order to actually fetch a value, all bundle specifiers need to be evaluated relative to a specific item record. It's not enough to ask to the description of an object record. We need to know which object record.

There are two ways to load a record for "getting" of data:

  1. Model instances - every table in the CA database has a corresponding model class that when instantiated can represent a single row in that table. The model includes methods for writing data and many utility functions as well as an interface for fetching data. If you need to get data from a single row and have either the row's id or some other intrinsic value that uniquely identifies the row then a model instance is a good choice.
  2. Search engine - use the search engine to select rows for "getting" of data if you need to get values from many rows and there is a search expression that can cleanly select the desired items.

Model instances and search result objects (as well as browse result objects) provide identical get() methods for getting of data. The method takes two parameters: a mandatory bundle specifier and an array of options, if required.

Examples of code using get with either class are shown below:

 // instantiate a model 
 $t_object = new ca_objects(40);   // load ca_object record with object_id = 40
 print "The title of the object is ".$t_object->get('ca_objects.preferred_labels.name')."<br/>\n";    // get the preferred name of the object
 
 // do a search and print out the titles of all found objects
 $o_search = new ObjectSearch();
 $qr_results = $o_search->search("Dreamland Park");    // ... or whatever text you like
 
 $count = 1;
 while($qr_results->nextHit()) {
     print "Hit ".$count.": ".$qr_results->get('ca_objects.preferred_labels.name')."<br/>\n";
     $count++;
 }

In the examples above the values returned are text ready for display in the user's current locale. Multiple values, from repeating attributes, multiple non-preferred labels or from several related items, are concatenated into a string using a delimiter.

By default get() always returns a string. You can use the options array parameter of get() to change how values are returned. The settings of two options – returnAsArray and returnAllLocales – are primarily responsible for the form of the returned value. Other options control the format and content of the returned values.

The key options are:

Option Description
returnAsArray If set to true value will be returned as an array with repeating values separated. The array is a simple integer-indexed array of values if returnAllLocales is false. If returnAllLocales is true then the returned array will be indexed first by integer index and then by locale_id, with values keyed on locale.
returnAllLocales If set to true then values for all locales will be returned rather than only in the current user's
delimiter Used to set the character(s) placed between repeating value when preparing for simple text output because returnAsArray is false. This setting has not effect when returnAsArray is false
template An optional bundle display template used to format the values returned by get(). If returnAsArray is set an array of links is returned. If returnAllLocales is set then template is ignored. If returnAsLink is set and the template includes <l> and </l> tags, only content within those tags will be returned as HTML links.
returnAsLink If set to true any values fetched from related rows will be returned as HTML links to the related rows. In Providence links will be to the appropriate editor; in Pawtucket links will be to the appropriate detail page. If returnAsArray is set an array of links is returned. If returnAllLocales is set then returnAsLink is ignored.
returnAsLinkTarget Optional parameter that causes links to be generated by a plug-in rather than the standard Providence or Pawtucket link generators. The target you pass here is defined in the plugin you wish to use. Ex. The FindingAids plugin in Pawtucket defines a 'FindingAids' target. If passed as a target, links use the plugin's link generator and the result are links to other pages generated by the plugin rather than standard Pawtucket detail pages. (Available from v1.4)
restrictToRelationshipTypes A list of relationship type id's or type codes. If specified then when getting related items only those related to the item at hand by relationships with the specified types will be fetched
excludeRelationshipTypes A list of relationship type id's or type codes. When specified get() will return related items that do not include the provided types.
locale If set, get() will try to return values in the specified languages rather than the language of the current user. Note that this is only a suggestion. If no values in the specified language are available, then the value will be returned in whatever language is available.
convertCodesToDisplayText By default get() will return list codes rather than item text suitable for display. If this is set to true then list items will be returned as their ca_list_item_labels display value.
convertLineBreaks If set to true will convert returns to <p> and <br/> HTML to ensure proper display.
sort An optional array of fields to sort by. Sorting is currently restricted to simple get()'s for related tables and can be done on returned fields only (intrinsic fields + label fields). If you are calling get on a ca_objects record, for example, to get a list of related entities, you can sort the returned values by surname like so:
print $t_object->get('ca_entities', array('sort' => array('ca_entity_labels.surname'));
Sorting is always in ascending order. You may sort on several fields if required.

For information on options relating to the hierarchy specifier see the Traversing hierarchical items section above.

For example, to print an array of all values in all languages of the preferred label for objects:

  // do a search and print out the titles of all found objects
 $o_search = new ObjectSearch();
 $qr_results = $o_search->search("Sea Gate");    // ... or whatever text you like
 
 // dump preferred labels in all languages
 while($qr_results->nextHit()) {
     print_r($qr_results->get('ca_objects.preferred_labels.name', array('returnAllLocales' => true, 'returnAsArray' => true)))";
 }
 
 // dump preferred labels in just the current language
 while($qr_results->nextHit()) {
     print_r($qr_results->get('ca_objects.preferred_labels.name', array('returnAllLocales' => false, 'returnAsArray' => true)))";
 }
 
 // dump preferred labels in all languages as a simple string delimited by semicolons (";")
 while($qr_results->nextHit()) {
     print_r($qr_results->get('ca_objects.preferred_labels.name', array('returnAllLocales' => false, 'returnAsArray' => false, 'delimiter' => '; ')))";  // you could omit returnAllLocales and returnAsArray since the defaults are false
 }

When only returnAsArray is enabled, but not returnAllLocales, the returned array will be a simple numerically indexed list of values. The values may be complex, however, based upon the nature of the bundle being fetched. Intrinsics will be simple string or numeric values while complex attributes will be arrays with keys set to element codes and values corresponding to those codes. Repeating values will be in numerically indexed value lists.

When returnAllLocales is return the returned array will be multi-dimensional: the first key will be the item_id (the unique internal identifier for the item itself), the second key will be the locale_id (as defined in the ca_locales table). The value of the second key will be the value which will be either a discrete value, an array with keys set to field names and corresponding values or a numerically indexed array of values (if the bundle being fetched is repeating, such as an attribute or non-preferred label).

If this sounds complicated, that's because it is a bit. Perhaps the best way to understand the return array structures is to print_r() the returned values and study the output. However, keep in mind that the default behavior of get() is usually what you want: a text value in the current locale ready for display. Only if you set either the returnAsArray or returnAllLocales options (but not both – returnAllLocales will take precedence if you do) will you receive an array. The combinations of options and corresponding return values are thus:

- returnAsArray = false returnAsArray = true
returnAllLocales = false String Array
returnAllLocales = true Array Array

Getting data from direct database queries using the Db class

You can execute any SQL query directly on the CA MySQL database using the Db class (app/lib/core/Db.php). Typical code to perform a SQL SELECT statement and print out identifiers is below:

 $o_data = new Db();
 $qr_result = $o_data->query("
    SELECT * 
    FROM ca_objects 
    WHERE idno LIKE '2008.%'
 ");
 
 while($qr_result->nextRow()) {
      print "GOT ACCESSION NUM=".$qr_result->get('idno')."<br/>\n";
 }

Note that direct queries do not use bundle specifiers. Rather simple field names – no table names or other elements – are used in the database. Only intrinsic fields or field in those tables you explicitly join in and fetch are available. All returned data will be "raw" as-stored in the database.

You should not use direct database queries (INSERT, UPDATE, DELETE) to change the database unless you know exactly what you are doing. Direct database write operations may cause search indices to go out of sync with database content or worse, cause data damage or loss.

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