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contain a NULL value We select data only from tbl_address in this view However, in some instances you may find yourself needing to display more customer data in addition to the address data for example, the customer_id column If this is the case, you need to join the two tables In this instance we have no need for additional information, so we forgo the join and save a little on resources Because we have these two views, the application developers can decide which one they need to reference in different places in their application and retrieve only the data they absolutely need
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The same rule goes for stored procedures as for views When you create stored procedures, think in terms of the entities they are meant to affect Doing so will help you avoid the pitfalls we discussed earlier around writing stored procedures to simply insert, update, or delete data Consider creating standards that govern how and why stored procedures are created, what entities are being affected, and what the potential data manipulations are How do you correctly implement stored procedures in your abstraction layer There are a great many correct answers to this question, because it depends on the environment and on your preferences We look at some of your options here, but remember that this is not the absolute correct answer in every situation A commonly used option is to create a single stored procedure for each entity; the procedure will update or insert data in all the associated tables This is usually the least confusing option, but it can make for some tricky code First, let s walk through the logical steps that a stored procedure must perform to save changes to a Customer entity in the Mountain View Music database, and then we will look at some code When the stored procedure runs, it must first determine whether or not a record already exists Luckily, you followed good modeling guidelines, so each and every table has a primary key defined, and that makes this step easy If the record exists it should be updated; otherwise, it should be inserted In addition, the stored procedure should return any information about what it did and which record was updated Sound simple It can be if you do your job correctly The following is an example of a stored procedure that performs the process we just dis-
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cussed for our Customer entity It writes to both the tbl_customer and the tbl_address table in our database
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ALTER PROCEDURE prc_save_customer @email varchar(50) ,@customer_id char(10) ,@firstname varchar(50) ,@lastname varchar(50) ,@homephone varchar(15) ,@workphone varchar(15) ,@mobilephone varchar(15) ,@addresses CustomerAddress ReadOnly ,@customer_objid int OUTPUT AS MERGE tbl_customer AS pri_customer USING ( SELECT customer_id = @customer_id ) AS source_customer(customer_id) ON ( pri_customercustomer_id = source_customercustomer_id ) WHEN NOT MATCHED THEN INSERT (email, customer_id, firstname, lastname, homephone, workphone, mobilephone) VALUES (@email, @customer_id, @firstname, @lastname, @homephone, @workphone, @mobilephone)
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WHEN MATCHED THEN UPDATE SET email=@email, firstname=@firstname, lastname=@lastname, homephone=@homephone, workphone=@workphone, mobilephone=@mobilephone; SELECT @customer_objid = objid FROM tbl_customer WHERE customer_id = @customer_id; MERGE tbl_address AS current_addresses USING ( SELECT customer_objid = @customer_objid, address_label, addressline1, addressline2, city, region, country, zipcode, is_deleted FROM @addresses ) AS source_addresses(customer_objid, address_label, addressline1, addressline2, city, region, country, zipcode, is_deleted) ON ( current_addressesaddress_label = source_addressesaddress_label AND current_addressescustomer_objid =
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source_addressescustomer_objid ) WHEN NOT MATCHED THEN INSERT (address_label, addressline1, addressline2, city, region, country, zipcode, customer_objid) VALUES (source_addressesaddress_label, source_addressesaddressline1, source_addressesaddressline2, source_addressescity, source_addressesregion, source_addressescountry, source_addresseszipcode, @customer_objid) WHEN MATCHED AND source_addressesis_deleted = 1 THEN DELETE WHEN MATCHED THEN UPDATE SET address_label=source_addressesaddress_label, addressline1=source_addressesaddressline1, addressline2=source_addressesaddressline2, city=source_addressescity, region=source_addressesregion, country=source_addressescountry, zipcode=source_addresseszipcode;
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This stored procedure may look a little complex, but it is really simple Using the MERGE statement, which is new in SQL Server 2008, we can write a single statement for each table MERGE evaluates the tables based on the provided values to determine whether the record in question is new and needs to be inserted, or whether it is an existing record that needs to be updated Also notice that one of the parameters being passed is called CustomerAddress This is a user-defined table data type being passed to the procedure as a table-valued parameter Table-valued parameters, also new to SQL Server 2008, allow us to pass multiple addresses for a customer using a single parameter
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