预定义类

The Relational DAS provides two classes: the Relational DAS itself and the subclass of Exception that can be thrown. The Relational DAS has four publicly useful calls: the constructor, the createRootDataObject call to obtain the root object of an empty data graph, the executeQuery call to obtain a data graph containing data from a relational database, and the applyChanges call to write changes made to a data graph back to the relational database.

SDO_DAS_Relational

The only object other than an SDO_DAS_Relational_Exception with which the application is expected to interact.

方法

  • __construct - construct the Relational DAS with a model derived from the passed metadata

  • createRootDataObject - obtain an otherwise empty data graph containing just the special root object

  • executeQuery - execute an SQL query passed as a literal string and return the results as a normalised data graph

  • executePreparedQuery - execute an SQL query passed as a prepared statement, with a list of values to substitute for placeholders, and return the results as a normalised data graph

  • applyChanges - examine the change summary in the data graph and apply those changes back to the database, subject to an assumption of optimistic concurrency

SDO_DAS_Relational_Exception

Is a subclass of PHP's Exception. It adds no behaviour to Exception. Thrown, with useful descriptive text, to signal errors in the metadata or unexpected failures to perform SQL operations.

SDO_DAS_Relational::applyChanges

Applies the changes made to a data graph back to the database

说明

void SDO_DAS_Relational::applyChanges ( PDO $database_handle , SDODataObject $root_data_object )

Warning

此函数是实验性的。此函数的表象,包括名称及其相关文档都可能在未来的 PHP 发布版本中未通知就被修改。使用本函数风险自担 。

Given a PDO database handle and the special root object of a data graph, examine the change summary in the datagraph and applies the changes to the database. The changes that it can apply can be creations of data objects, deletes of data objects, and modifications to properties of data objects.

参数

PDO_database_handle
Constructed using the PDO extension. A typical line to construct a PDO database handle might look like this:

$dbh = new PDO("mysql:dbname=COMPANYDB;host=localhost",DATABASE_USER,DATABASE_PASSWORD);

root_data_object
The special root object which is at the top of every SDO data graph.

返回值

None. Note however that the datagraph that was passed is still intact and usable. Furthermore, if data objects were created and written back to a table with autogenerated primary keys, then those primary keys will now be set in the data objects. If the changes were successfully written, then the change summary associated with the datagraph will have been cleared, so that it is possible to now make further changes to the data graph and apply those changes in turn. In this way it is possible to work with the same data graph and apply changes repeatedly.

错误/异常

SDO_DAS_Relational::applyChanges can throw an SDO_DAS_Relational_Exception if it is unable to apply all the changes correctly.

The Relational DAS starts a database transaction before beginning to apply the changes and will commit the transaction only if they are all successful. The Relational DAS generates qualified update and delete statements which contain a where clause that specifies that the row to be updated or deleted must contain the same values that it did when the data was first retrieved. This is how the optimistic concurrency is implemented. If any of the qualified update or delete statements fails to update or delete their target row, it may be because the data has been altered in the database in the meantime. In any event, if any update fails for any reason, the transaction is rolled back and an exception thrown. The exception will contain the generated SQL statement that failed.

The Relational DAS also catches any PDO exceptions and obtains PDO diagnostic information which it includes in an SDO_DAS_Relational_Exception which it then throws.

范例

Please see the Examples section in the general information about the Relational DAS for many examples of calling this method. Please see also the section on Tracing to see how you can see what SQL statements are generated by the Relational DAS.

SDO_DAS_Relational::__construct

Creates an instance of a Relational Data Access Service

说明

SDO_DAS_Relational::__construct ( array $database_metadata [, string $application_root_type [, array $SDO_containment_references_metadata ]] )

Warning

此函数是实验性的。此函数的表象,包括名称及其相关文档都可能在未来的 PHP 发布版本中未通知就被修改。使用本函数风险自担 。

Constructs an instance of a Relational Data Access Service from the passed metadata.

参数

database_metadata
An array containing one or more table definitions, each of which is an associative array containing the keys name, columns, PK, and optionally, FK. For a full discussion of the metadata, see the metadata section in the general information about the Relational DAS.

application_root_type
The root of each data graph is an object of a special root type and the application data objects come below that. Of the various application types in the SDO model, one has to be the application type immediately below the root of the data graph. If there is only one table in the database metadata, so the application root type can be inferred, this argument can be omitted.

SDO_containment_references_metadata
An array containing one or more definitions of a containment relation, each of which is an associative array containing the keys parent and child. The containment relations describe how the types in the model are connected to form a tree. The type specified as the application root type must be present as one of the parent types in the containment references. If the application only needs to work with one table at a time, and there are no containment relations in the model, this argument can be omitted. For a full discussion of the metadata, see the metadata section in the general information about the Relational DAS.

返回值

Returns an SDO_DAS_Relational object on success.

错误/异常

SDO_DAS_Relational::__construct throws a SDO_DAS_Relational_Exception if any problems are found in the metadata.

范例

For a full discussion of the metadata, see the metadata section in the general information about the Relational DAS.

SDO_DAS_Relational::createRootDataObject

Returns the special root object in an otherwise empty data graph. Used when creating a data graph from scratch

说明

SDODataObject SDO_DAS_Relational::createRootDataObject ( void )

Warning

此函数是实验性的。此函数的表象,包括名称及其相关文档都可能在未来的 PHP 发布版本中未通知就被修改。使用本函数风险自担 。

Returns the special root object at the top of an otherwise empty data graph. This call is used when the application wants to create a data graph from scratch, without having called executeQuery to create a data graph.

The special root object has one multi-valued containment property, with a name of the application root type that was passed when the Relational DAS was constructed. The property can take values of only that type. The only thing that the application can usefully do with the root type is to call createDataObject on it, passing the name of the application root type, in order to create a data object of their own application type.

参数

None.

返回值

The root object.

错误/异常

None.

范例

Please see the Examples section in the general information about the Relational DAS for many examples of calling this method.

SDO_DAS_Relational::executePreparedQuery

Executes an SQL query passed as a prepared statement, with a list of values to substitute for placeholders, and return the results as a normalised data graph

说明

SDODataObject SDO_DAS_Relational::executePreparedQuery ( PDO $database_handle , PDOStatement $prepared_statement , array $value_list [, array $column_specifier ] )

Warning

此函数是实验性的。此函数的表象,包括名称及其相关文档都可能在未来的 PHP 发布版本中未通知就被修改。使用本函数风险自担 。

Executes a given query against the relational database, using the supplied PDO database handle. Differs from the simpler executeQuery in that it takes a prepared statement and a list of values. This is the appropriate call to use either when the statement is to executed a number of times with different arguments, and there is therefore a performance benefit to be had from preparing the statement only once, or when the SQL statement is to contain varying values taken from a source that cannot be completely trusted. In this latter case it may be unsafe to construct the SQL statement by simply concatenating the parts of the statement together, since the values may contain pieces of SQL. To guard against this, a so-called SQL injection attack, it is safer to prepare the SQL statement with placeholders (also known as parameter markers, denoted by '?') and supply a list of the values to be substituted as a separate argument. Otherwise this function is the same as executeQuery in that it uses the model that it built from the metadata to interpret the result set and returns a data graph.

参数

PDO_database_handle
Constructed using the PDO extension. A typical line to construct a PDO database handle might look like this:

$dbh = new PDO("mysql:dbname=COMPANYDB;host=localhost",DATABASE_USER,DATABASE_PASSWORD);

prepared_statement
A prepared SQL statement to be executed against the database. This will have been prepared by PDO's prepare method.

value_list
An array of the values to be substituted into the SQL statement in place of the placeholders. In the event that there are no placeholders or parameter markers in the SQL statement then this argument can be specified as NULL or as an empty array;

column_specifier
The Relational DAS needs to examine the result set and for every column, know which table and which column of that table it came from. In some circumstances it can find this information for itself, but sometimes it cannot. In these cases a column specifier is needed, which is an array that identifies the columns. Each entry in the array is simply a string in the form table-name.column_name.

The column specifier is needed when there are duplicate column names in the database metadata, For example, in the database used within the examples, all the tables have both a id and a name column. When the Relational DAS fetches the result set from PDO it can do so with the PDO_FETCH_ASSOC attribute, which will cause the columns in the results set to be labelled with the column name, but will not distinguish duplicates. So this will only work when there are no duplicates possible in the results set.

To summarise, specify a column specifier array whenever there is any uncertainty about which column could be from which table and only omit it when every column name in the database metadata is unique.

All of the examples in the Examples use a column specifier. There is one example in the Scenarios directory of the installation that does not: that which works with just the employee table, and because it works with just one table, there can not exist duplicate column names.

返回值

Returns a data graph. Specifically, it returns a root object of a special type. Under this root object will be the data from the result set. The root object will have a multi-valued containment property with the same name as the application root type specified on the constructor, and that property will contain one or more data objects of the application root type.

In the event that the query returns no data, the special root object will still be returned but the containment property for the application root type will be empty.

错误/异常

SDO_DAS_Relational::executePreparedQuery can throw an SDO_DAS_Relational_Exception if it is unable to construct the data graph correctly. This can occur for a number of reasons: for example if it finds that it does not have primary keys in the result set for all the objects. It also catches any PDO exceptions and obtains PDO diagnostic information which it includes in an SDO_DAS_Relational_Exception which it then throws.

范例

示例 #1 Retrieving a data object using executePreparedQuery

In this example a single data object is retrieved from the database - or possibly more than one if there is more than one company called 'Acme'. For each company returned, the name and id properties are echoed.

Other examples of the use of executePreparedQuery can be found in the example code supplied in sdo/DAS/Relational/Scenarios.

<?php
require_once 'SDO/DAS/Relational.php';
require_once 'company_metadata.inc.php';

/**************************************************************
 * Construct the DAS with the metadata
 ***************************************************************/
$das = new SDO_DAS_Relational ($database_metadata,'company',$SDO_reference_metadata);

/**************************************************************
 * Get a database connection
 ***************************************************************/
$dbh = new PDO(PDO_DSN,DATABASE_USER,DATABASE_PASSWORD);

/**************************************************************
 * Issue a query to obtain a company object - possibly more if they exist
 * Use a prepared query with a placeholder.
 ***************************************************************/
$name = 'Acme';
$pdo_stmt = $dbh->prepare('select name, id from company where name=?');
$root = $das->executePreparedQuery(
    $dbh, 
    $pdo_stmt,
    array($name), 
    array('company.name', 'company.id'));

/**************************************************************
 * Echo name and id 
 ***************************************************************/
foreach ($root['company'] as $company) {
    echo "Company obtained from the database has name = " . 
    $company['name'] . " and id " . $company['id'] . "\n";
}
?>

SDO_DAS_Relational::executeQuery

Executes a given SQL query against a relational database and returns the results as a normalised data graph

说明

SDODataObject SDO_DAS_Relational::executeQuery ( PDO $database_handle , string $SQL_statement [, array $column_specifier ] )

Warning

此函数是实验性的。此函数的表象,包括名称及其相关文档都可能在未来的 PHP 发布版本中未通知就被修改。使用本函数风险自担 。

Executes a given query against the relational database, using the supplied PDO database handle. Uses the model that it built from the metadata to interpret the result set. Returns a data graph.

参数

PDO_database_handle
Constructed using the PDO extension. A typical line to construct a PDO database handle might look like this:

$dbh = new PDO("mysql:dbname=COMPANYDB;host=localhost",DATABASE_USER,DATABASE_PASSWORD);

SQL_statement
The SQL statement to be executed against the database.

column_specifier
The Relational DAS needs to examine the result set and for every column, know which table and which column of that table it came from. In some circumstances it can find this information for itself, but sometimes it cannot. In these cases a column specifier is needed, which is an array that identifies the columns. Each entry in the array is simply a string in the form table-name.column_name.

The column specifier is needed when there are duplicate column names in the database metadata. For example, in the database used within the examples, all the tables have both a id and a name column. When the Relational DAS fetches the result set from PDO it can do so with the PDO_FETCH_ASSOC attribute, which will cause the columns in the results set to be labelled with the column name, but will not distinguish duplicates. So this will only work when there are no duplicates possible in the results set.

To summarise, specify a column specifier array whenever there is any uncertainty about which column could be from which table and only omit it when every column name in the database metadata is unique.

All of the examples in the Examples use a column specifier. There is one example in the Scenarios directory of the installation that does not: that which works with just the employee table, and because it works with just one table, there can not exist duplicate column names.

返回值

Returns a data graph. Specifically, it returns a root object of a special type. Under this root object will be the data from the result set. The root object will have a multi-valued containment property with the same name as the application root type specified on the constructor, and that property will contain one or more data objects of the application root type.

In the event that the query returns no data, the special root object will still be returned but the containment property for the application root type will be empty.

错误/异常

SDO_DAS_Relational::executeQuery can throw an SDO_DAS_Relational_Exception if it is unable to construct the data graph correctly. This can occur for a number of reasons: for example if it finds that it does not have primary keys in the result set for all the objects. It also catches any PDO exceptions and obtains PDO diagnostic information which it includes in an SDO_DAS_Relational_Exception which it then throws.

范例

Please see the Examples section in the general information about the Relational DAS for many examples of calling this method.

目录