|By Jerry Dixon||
|March 14, 2006 10:00 AM EST||
These days, applications built around a service-oriented architecture (SOA) are all the rage. Complex systems can be written as a collection of services that communicate with each other through standard protocols. When implemented properly, these systems can become immensely flexible, scalable, and easy to maintain. The most common SOA designs utilize Web services as the communications medium, because they can be created and consumed by disparate systems and platforms. This highly useful capability has made Web services a very important part of today's information systems.
Up until now, the classic Microsoft implementation of a Web service involved a back-end database server running SQL Server 2000 and a front-end Web server running a .NET Web service application on IIS. Now that SQL Server 2005 is here, we have an additional option: we can create and host Web services using SQL Server alone. In this scenario, no Web server is needed. When running on Windows Server 2003 or Windows XP with Service Pack 2, IIS is not needed either. These operating systems provide the HTTP API, also known as HTTP.SYS, which SQL Server uses to provide native Web service functionality.
In this article I will show how to create a Web service inside SQL Server. I will show how to define the service and how to access it from a .NET client application. Along the way, we will see how incredibly flexible SQL Server's Web service support is. Hopefully, we will also gain an appreciation of how capable a tool SQL Server 2005 has become. Let's get started.
SQL Server 2005 provides Web services through endpoints. Endpoints define the properties of a connection, which can use either the HTTP or the TCP protocol. They can provide support for SOAP, Service Broker, and Database Mirroring. As you might guess, the syntax for creating a new endpoint is quite complex. Because of this, I am going to focus solely on the syntax required to create a Web service. Listing 1 shows an example of this. We'll walk through each line in detail.
Endpoints are created via the CREATE ENDPOINT statement. This statement consists of four main parts: endpoint name, the initial state, the AS clause, and the FOR clause.
Name and Initial State
The first two parts are easy: they provide a name for the endpoint and specify the state of the endpoint after it is created. The state can be STARTED, STOPPED, or DISABLED. STARTED indicates that the endpoint is actively listening for connections and will respond to connection attempts. STOPPED indicates that the endpoint will listen for connections and will respond to connection attempts, but will refuse the connection and return an error to the client. The last option, DISABLED, indicates that the endpoint will not listen for connections, nor will it respond to connection attempts. STOPPED is the default, but this can be changed either through the CREATE ENDPOINT statement or via an ALTER ENDPOINT statement at a later time.
The AS clause specifies the communications protocol that the endpoint will use. Here we have specified the HTTP protocol, which is the protocol required for a Web service. (TCP is an option for other types of services, and would have different settings than those described here.) The exact implementation details are controlled by a list of specific options included inside parentheses. Those used in our example are described here:
- PATH specifies the URL of the endpoint. This setting, along with the SITE setting described later, fully specifies the URL that will be used to invoke the Web service. (For example, I've used '/Employee,' so the URL would be HTTP://ServerName/Employee.)
- AUTHENTICATION specifies the type(s) of authentication that will be used. This is a comma-separated list of authentication methods, including those that we should all be familiar with: BASIC, DIGEST, NTLM, KERBEROS, and INTEGRATED. These work as expected, although additional in-depth information can be found in SQL Server Books Online. My example used Windows Integrated authentication only, so I've specified INTEGRATED.
- PORTS specifies the type of port to use: CLEAR and/or SSL. CLEAR indicates a non-encrypted port, which requires clients to use the HTTP protocol. SSL indicates an encrypted port, requiring clients to use the HTTPS protocol. If required, both settings can be used simultaneously. The example uses unencrypted HTTP communications, so the appropriate setting is CLEAR.
- CLEAR_PORT specifies the actual port that will be used by unencrypted communications. If not specified, port 80 is assumed. In this example, I've used port 8080 because my computer has IIS installed, which means that port 80 is already in use. There is also an SSL_PORT setting that we can use if needed, and it defaults to port 443. My example doesn't use SSL, so I haven't included this option.
- SITE determines the ServerName portion of the Web service URL. If we use an asterisk ("*"), it instructs the endpoint to use all possible host names that aren't explicitly reserved. I used this setting in my example so that both HTTP://localhost/Employee and HTTP://jdixon/Employee would work. If we use a plus sign ("+"), then the endpoint will use all possible host names, even if they are reserved. Finally, we could explicitly specify the host name, which would ensure that only that name would be used.
- COMPRESSION specifies whether client requests for compressed communications will be honored. If enabled, GZIP encoding will be used when client requests include the appropriate HTTP encoding header. Disabled is the default, and specifies that compression will not be used even if the client properly requests it. I've chosen to enable compression in the example, although I don't specifically need it.
The FOR clause specifies the service that the endpoint provides. This can be SOAP, SERVICE_BROKER, or DATABASE_MIRRORING. We want to create a Web service, so we must choose SOAP. (Once again, the possible settings vary greatly depending upon which option we choose, so I'm going to restrict my explanation to SOAP-specific settings. Consult Books Online for more details.) The FOR clause consists of one or more WEBMETHOD clauses followed by some service-wide settings.
The WEBMETHOD clause does exactly what you would expect; it defines a single Web method. If a Web service needs multiple methods, then multiple WEBMETHOD clauses will be needed. In our example, there are two methods. The two methods are quite similar; therefore, I'll describe just the first one.
The first part of the WEBMETHOD clause defines the name, or alias, of the method. The alias can also include a namespace, but this is optional. If the namespace is not included, then the namespace from the endpoint is used instead. (The endpoint's namespace will be described in a moment.) After the alias, additional settings are used to specify exactly how this method will function. Note that these settings are included inside parentheses, and that the parentheses are required.
- NAME specifies the fully-qualified name of the stored procedure or user-defined function that will be invoked by the method. The name must be in the standard database.owner.name format. My example uses a stored procedure named uspGetEmployeeManagers that is found in the AdventureWorks database, within the dbo schema.
- SCHEMA determines whether the SOAP message for this method will include an inline XSD schema. There are three options; NONE, STANDARD, and DEFAULT. NONE specifies that no schema will be used, while STANDARD specifies that one will. DEFAULT specifies that the setting from the endpoint itself should be used. If no value is specified, DEFAULT will be assumed.
- FORMAT determines the exact content of the method response. The options are ALL_RESULTS, ROWSETS_ONLY, and NONE. ALL_RESULTS instructs the method to return not only the output from the stored procedure or user-defined function, but also the row count and any error messages or warnings that may exist. ROWSETS_ONLY omits everything but the actual results. NONE suppresses the results too, making this option useful only in very specific circumstances (see SQL Books Online for details). The example uses ROWSETS_ONLY.
The final four settings apply to the whole Web service, and not to a specific method:
- BATCHES specifies whether ad hoc T-SQL statements can be executed via this service. DISABLED, the default, prevents this. ENABLED allows it. When enabled, a special method called SQLBATCH will be created that supports ad hoc queries.
- WSDL determines the type of WSDL (Web Services Definition Language) document that the Web service will generate. A value of NONE prevents the WSDL from being generated. DEFAULT, on the other hand, directs that the WSDL will be generated. In those rare cases where a special WSDL document is needed, you can specify the name of a stored procedure that returns the special document.
- DATABASE identifies the name of the database context against which the Web methods will be executed. Our service uses the AdventureWorks database, so that name is included here. If DEFAULT is specified instead, then the default database for the login will be used.
- NAMESPACE specifies the namespace for the endpoint. If DEFAULT is used, or if no namespace is specified, then the namespace will be HTTP://tempuri.org. If a namespace is included at the WEBMETHOD level, then that namespace will override the one provided here.
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