Developing the Joomla! Component and Understanding. We understand your time is important. Educational Testing Service (ETS) Who We Serve; Research; Our Mission; Who We Serve. From students and teachers to administrators and employers, at ETS we provide a range of solutions designed to meet the many different. Uniquely amongst the major publishers, we seek to develop and publish the broadest range of learning and information products on each technology. Understanding Valuation and Insurance Options BrochureProtecting Your Household Goods. Registration; Safety; FMCSA News; FMCSA Portal. Arcserve-KB : Understanding arcserve Backup for. Understanding Enterprise Services (COM+) in . NET. Familiarity with Enterprise Services is not necessary but would be helpful. For a good background on these topics, refer to. COM provides one way to write component- based applications. It is well known that the plumbing work required to write COM components is significant and repetitive. COM+ is not so much about a new version of COM; rather, COM+ provides a services infrastructure for components. Components are built and then installed in COM+ applications in order to build scalable server applications that achieve high throughput with ease of deployment.
Scalability and throughput is achieved by designing applications from the outset to make use of services such as transactions, object pooling and activity semantics. The . NET Framework provides another way to write component- based applications and has the advantages over the COM programming model of better tool support, the common language runtime (CLR), and a much easier coding syntax. The COM+ services infrastructure can accessed from managed and unmanaged code. Services in unmanaged code are known as COM+ services. In . NET, these services are referred to as Enterprise Services. Deriving a class from Serviced. Component indicates that services will be required for a component. Tool support has improved to enable programmers to write server based applications yet the same issues of scalability and throughput are still in the realm of good programming practices. The basic idea behind services is design for throughput and scalability from the outset and leverage Enterprise Services to easily implement those design patterns where appropriate. It could be argued that the services infrastructure design actually has little to do with COM or even components: COM+ services can now be applied to COM components, to . NET components, and even to other entities that are not considered components, such as ASP pages or arbitrary code blocks (see the Services without Components COM+ feature on Microsoft Windows. Some of these services include, transactions, object pooling and construction strings, JIT, synchronization, role- based security, CRM and BYOT. For a complete listing of services on Microsoft Windows. Microsoft Windows XP includes a new version of COM+, namely COM+ 1. NET components. Transactions. In order to write managed applications that use services, classes requiring services must derive from Serviced. Component and use various custom attributes to specify the actual services required. This section introduces these concepts and how they affect writing managed code. A more detailed explanation is provided in later sections. Suppose a class Account has been written (the actual code is listed later) and is located in the Bank. Component assembly. This class could be used as follows: Bank. Component Client. Bank. Component. namespace Bank. Component. Client. In addition, a reference must be added for the System. Enterprise. Services assembly. This is a general . NET requirement when a derived class does not override all the base class methods. The Bank. Component Server code shows the implementation of the Account class in . NET, which uses transactions. The class Account derives from the class System. Enterprise. Services. Serviced. Component. The Transaction attribute marks the class as requiring a transaction. The Synchronization and JIT services are configured automatically because the Transaction attribute is used. The Auto. Complete attribute is used to specify that the runtime must automatically call the Set. Abort function for the transaction if an unhandled exception is thrown during the execution of the method; otherwise, a Set. Complete function is called. The Application. Name attribute associates this assembly with a COM+ application that stores the service configuration data for this application. Further modifications that are required for this class are highlighted in the code. Bank. Component Server. System. Enterprise. Services. . A summary of the complete process from coding to deployment is listed below. Write the server assembly. Build the assembly. Sign the assembly. A key file can be generated once for the project. It is not necessary to generate one for each compilation. A key can be created using the Microsoft . NET command prompt and sn. Compile the code. A reference must be added for System. Enterprise. Services. Deploy the application. The Serviced. Component class and the custom attributes are the two key concepts for gaining access to COM+ services from managed code. The configuration of the service is stored in the COM+ catalog. The objects reside and execute within the CLR. The managed object and its associated COM+ context is depicted in Figure 1 and will become clearer in the next two sections. Services associated with managed components. With COM+ components you need to configure the catalog manually, but with serviced components, the catalog can be updated based on the attributes in the code. An assembly can be explicitly registered using the command line tool regsvcs. API. More details are provided in the deployment details section below. During development, XCopy deployment is provided as a convenience by simply copying the assembly into the application directory. Whenever a client application creates instances of classes derived from Serviced. Component, the runtime detects whether or not it has already registered the assembly in a COM+ application. If it has not been registered, the local directory is searched for the assembly and if found, all the serviced components in the assembly are registered in a COM+ application and the activation can then proceed. This is known as lazy registration but it does not work for all scenarios. For instance, assemblies that are marked as a COM+ server app require explicit registration (see below), and lazy registration does not work for unmanaged clients calling managed serviced components. Lazy registration is useful during development time, otherwise use scripts, code or Reg. Svcs to register the assembly. Possibly place the assembly in the GAC. See the deployment section for more details. Run the client. Deployment. Custom attributes are one of the two key concepts of accessing COM+ services from managed code. Custom attributes are used to specify the services that are required, such as the Transaction custom attribute in the previous code listing. These attributes store the configuration options for a service in the assembly metadata. The custom attributes are used by having some code load the assembly and using reflection, create instances of the attributes and call methods on the attribute to extract the service configuration stored in the attribute. The information can then be written to the COM+ catalog. The code that performs these and other steps is contained in Enterprise. Services. Registration. Helper. In order to make the process of registration easier, all forms of registration use the component Enterprise. Services. Registration. Helper. This component is accessible as a managed class as well as a COM object. Figure 2. Registering serviced components. Conceptually, Registration. Helper performs the following steps. Uses Registration. Services. Register. Assembly to register the assembly in the registry. Therefore, classes appear in the registry as COM components written in managed code and have the Inproc. Server. 32 key pointing to mscoree. If a managed class does not implement any interfaces, the class's public methods do not appear in the COM+ catalog, unless the Class. Interface. Attribute is used. This means that service configuration associated with the method level cannot be stored in the catalog. However, some COM+ services can be configured at the method level and require the component to expose an interface as viewed in the COM+ catalog. For example, COM+ role- based security on the method level requires a component to implement an interface in order to configure the service. More is discussed about this issue in the security section. Generates a COM type library from the assembly using Type. Lib. Converter. Convert. Assembly. To. Type. Lib. Registers the type library. So far, this is very much the same as Reg. Asm. exe /tlb. Finds or creates a COM+ application. The name is extracted from the Application. Name attribute, the assembly name or the supplied application name/GUID. Uses the type library to configure the COM+ application using the COM+ admin APIs. Goes through all the custom attributes and uses IConfiguration. Attribute to write configuration data for the particular service to the COM+ catalog. Registration. Helper will attempt to do theses steps within a transaction using Registration. Helper. Tx, a class within a COM+ application that is created when . NET is installed. Therefore, if registration fails, the COM+ catalog and registry will be restored to their original state. Currently, the generated type libraries will however remain on disk (or in the GAC if the assembly was in the GAC). If the assembly being registered references other assemblies that also use COM+ services, all assemblies in the dependency graph will undergo the same steps as listed above. Since Registration. Helper accesses the COM+ catalog, it requires unmanaged code permissions and admin rights on the machine. Therefore, the same is true for clients to Registration. Helper namely: lazy registration, Reg. Svcs or your scripts/code. This also implies that code downloaded from the Internet or stored on a network share cannot be registered. It is possible to code incompatible attribute combinations, such as requiring a transaction and setting synchronization to disabled. These combinations are currently detected during registration time when writing them to the COM+ catalog and not during compile time. When a managed component is registered, the COM+ catalog default values are used unless attributes are used to overwrite the 'unconfigured' default values.
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