- 1-2 Key Features of the Object-Relational Model. - Introduces the key features and explains the advantages of the object-relational model.. - Enter one of the options. - That you can repeat a portion of the code. - Key Features of the Object-Relational Model. - Oracle implements the object-type system as an extension of the relational model.. - This section lists the key features and concepts of the object-relational model that are related to the database.. - Methods are procedures or functions provided to enable applications to perform useful operations on the attributes of the object type. - An instantiation of the object type creates an object built according to the template. - When you create a variable of an object type, you create an instance of the type and the result is an object. - A constructor method is called on a type to construct or create an object instance of the type.. - As a multi-column table in which each attribute of the object type person_typ . - data—rows for both the type of the view and for its subtypes.. - A REF can be scoped to an object table of the declared type (person_typ in the example) or of any subtype of the declared type. - If scoped to an object table of a subtype, the REF column is effectively constrained to hold references only to instances of the subtype (and its subtypes, if any) in the table.. - But in the first case, Oracle allocates space for an object in the contact column and sets each of the object's attributes to NULL. - The first example places a PRIMARY KEY constraint on the idno column of the object table person_extent : CREATE TYPE location_typ. - In the second SELECT statement, idno is the name of an attribute of the person_typ object in the column named contact . - You cannot use a database link to do any of the following:. - The name of the constructor method is just the name of the object type, as shown in the following simple example:. - whenever an instance of the subtype invokes the method. - implementations of the same method. - Subtypes of the current type are not searched.. - description, and category_id attributes of the category_typ supertype.. - This version of the student_typ subtype is substitutable. - typ from the declared type of the view, person_typ:. - The syntax of the function is:. - It gets the name attribute and typeid of the object instances in the person_obj_table table. - Each of the instances is of a different type:. - You query table functions by using the TABLE keyword before the function name in the FROM clause of the query.. - corresponding to rows of the table or view. - The name of a type's constructor method is simply the name of the type. - The following example illustrates a literal invocation of the constructor method for the nested table type people_typ.. - A nested table is an unordered set of data elements, all of the same datatype. - No maximum is specified in the definition of the table and the order of the elements is not preserved. - If the column in a nested table is an object type, the table can also be viewed as a multi-column table, with a column for each attribute of the object type.. - When a column in a relational table is of nested table type, Oracle stores the nested table data for all rows of the relational table in the same storage table. - If the TABLESPACE clause is not specified, then the storage table of the nested table is created in the tablespace where the parent table is created. - Constructor parameters have the names and types of the object type's attributes.. - nests the elements of the collection in the result row with which the collection is associated.. - Updating elements of the collection.. - For example, suppose v_planets is a variable declared to be of the planets nested table type nt_pl_t. - where person_typ (12, 'Bob Jones is an element of the same type as the elements of the nested table math_majors.. - on page 2-35 for an example of the COLLECT function. - Oracle Database SQL Reference for syntax of the COLLECT function. - The limit on the cardinality of the multiset argument is 32.. - submultisets of a nested table of the specified cardinality. - The limit on the cardinality of the nested table argument is 32.. - The nested table returned is of the same named type as the input nested table.. - Manage the size of the object cache's memory.. - For example, to manipulate instances of the object types in a C program, you must represent these types in the C host language format. - You can use a tool provided by Oracle called the Object Type Translator (OTT) to generate the C mapping of the object types. - The following Visual Basic example illustrates how to access attributes of the Address object in the person_tab table:. - The following Visual Basic example illustrates how to access attributes of the EnameList object from the department table:. - SQLJ types use the corresponding Java class as the body of the type. - In a SQL representation, the attributes of the type are stored in columns like attributes of ordinary object types. - If the object's class is a superclass of the attribute's type/class, an error is raised. - For the return type of the function, specify the Java type mapped to the SQL type.. - Define an object type, where each attribute of the type corresponds to an existing column in a relational table.. - Specify a unique value, based on attributes of the underlying data, to serve as an object identifier, which enables you to create pointers (REFs) to the objects in the view. - synthesize the principal object instances of the view. - The address objects are constructed from columns of the relational table.. - An object type (for example, emp_t) is defined to correspond to each relational table, with attributes whose types correspond to the types of the. - In the view, the deptno column becomes the deptno attribute of the object type. - In the example we have been developing, each object selected out of the dept_. - many-to-one side of the relationship can be modeled using object references.. - Oracle updates the base tables of the object view if there is no ambiguity.. - We implement the trigger by means of the following code:. - For example, in the case of the department and employee, the department object currently includes a list of employees. - Any subview must be based on a direct subtype of the type of its direct superview.. - If you specify individual attributes of the view's declared type in the SELECT list or do a SELECT. - The ONLY keyword confines the selection to the declared type of the view that you are querying:. - Declare a variable or parameter of the named type.. - Selecting columns of an object table does not require privileges on the type of the object table. - For example, the following statement causes syn1 to point to type typ2 instead of the type it formerly pointed to:. - Some of the key performance factors are the following:. - Java in the Database. - Export writes object type definitions and all of the associated data to the dump file. - Each of these leaf-level attributes of the original object type is stored in a table column.. - The leaf-level attributes that are not collection types are called the leaf-level scalar attributes of the object type.. - You must declare these tables as part of the object table declaration. - It will also have hidden columns for attributes of the subtypes of person_typ. - These retrofit the tables to store data of the new type. - You can build an index on attributes of any of the types that can be stored in a substitutable column. - Here the values stored in the hidden column for major may be different from the results of the TREAT expression. - In any case, table data is always returned in the format of the latest type version. - You can retrieve the definition of the latest type from the system view USER_. - conversion of the related data.. - The column can then store subtype instances of the altered type.. - Table 7–1 lists some of the important options in the ALTER TYPE statement for altering the attribute or method definition of a type.. - Converts data stored in all user-defined columns to the most recent version of the column's type.. - Only the metadata of the column is marked unused. - See Table 7–1 on page 7-16 for a discussion of the INCLUDING DATA option.. - In your definition of the constructor, you can initialize the attributes to any appropriate values. - The mode of each of the user-defined constructor's parameters (after the implicit SELF parameter) must be IN.. - Note that, if you evolve a type—for example, by adding an attribute—the signature of the type's attribute-value constructor changes accordingly. - encapsulated information into parameters of the generic types. - In the body of the procedure, you can detail how to handle the encapsulated data and type. - You can query the data of the underlying datatypes like any other data.. - User-defined aggregates are a feature of the Extensibility Framework
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