Filtering Values Using sql:limit-field and sql:limit-value [SQLXML 4.0]
You can limit rows that are returned from a database query on the basis of some limiting value. The sql:limit-field and sql:limit-value annotations are used to identify the database column that contains limiting values and to specify a specific limiting value to be used to filter the data returned.
The sql:limit-field annotation is used to identify a column that contains a limiting value; it is allowed on each mapped element or attribute.
The sql:limit-value annotation is used to specify the limited value in the column that is specified in the sql:limit-field annotation. The sql:limit-value annotation is optional. If sql:limit-value is not specified, a NULL value is assumed.
[!NOTA] When working with a sql:limit-field where the mapped SQL column is of type real, SQLXML 4.0 performs conversion on the sql:limit-value as specified in XML schemas as an nvarchar specified value. This requires that decimal limit values be specified using full scientific notation. For more information, see Example B below.
Examples
To create working samples using these examples, you need to have the following installed:
- Microsoft SQL Native Client
- MDAC 2.6 or later
In these examples, templates are used to specify XPath queries against the mapping XSD schema.
A. Limiting the customer addresses returned to a specific address type
In this example, a database contains two tables:
- Customer (CustomerID, CompanyName)
- Addresses (CustomerID, AddressType, StreetAddress)
A customer can have a shipping address and/or a billing address. The AddressType column values are Shipping and Billing.
This is the mapping schema in which the ShipTo schema attribute maps to the StreetAddress column in the Addresses relation. The values that are returned for this attribute are limited to only shipping addresses by specifying the sql:limit-field and sql:limit-value annotations. Similarly, the BillTo schema attribute returns only the billing address of a customer.
This is the schema:
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:sql="urn:schemas-microsoft-com:mapping-schema">
<xsd:annotation>
<xsd:appinfo>
<sql:relationship name="CustAddr"
parent="Customer"
parent-key="CustomerID"
child="Addresses"
child-key="CustomerID" />
</xsd:appinfo>
</xsd:annotation>
<xsd:element name="Customer" sql:relation="Customer" >
<xsd:complexType>
<xsd:sequence>
<xsd:element name="BillTo"
type="xsd:string"
sql:relation="Addresses"
sql:field="StreetAddress"
sql:limit-field="AddressType"
sql:limit-value="billing"
sql:relationship="CustAddr" >
</xsd:element>
<xsd:element name="ShipTo"
type="xsd:string"
sql:relation="Addresses"
sql:field="StreetAddress"
sql:limit-field="AddressType"
sql:limit-value="shipping"
sql:relationship="CustAddr" >
</xsd:element>
</xsd:sequence>
<xsd:attribute name="CustomerID" type="xsd:int" />
<xsd:attribute name="CompanyName" type="xsd:string" />
</xsd:complexType>
</xsd:element>
</xsd:schema>
To test a sample XPath query against the schema
Create two tables in the tempdb database:
USE tempdb CREATE TABLE Customer (CustomerID int primary key, CompanyName varchar(30)) CREATE TABLE Addresses(CustomerID int, StreetAddress varchar(50), AddressType varchar(10))Add the sample data:
INSERT INTO Customer values (1, 'Company A') INSERT INTO Customer values (2, 'Company B') INSERT INTO Addresses values (1, 'Obere Str. 57 Berlin', 'billing') INSERT INTO Addresses values (1, 'Avda. de la Constitución 2222 México D.F.', 'shipping') INSERT INTO Addresses values (2, '120 Hanover Sq., London', 'billing') INSERT INTO Addresses values (2, 'Forsterstr. 57, Mannheim', 'shipping')Copy the schema code above and paste it into a text file. Save the file as LimitFieldValue.xml.
Create the following template (LimitFieldValueT.xml), and save it in the same where you saved the schema (LimitFieldValue.xml) in the previous step:
<ROOT xmlns:sql="urn:schemas-microsoft-com:xml-sql"> <sql:xpath-query mapping-schema="LimitFieldValue.xml"> /Customer </sql:xpath-query> </ROOT>The directory path specified for the mapping schema (LimitFieldValue.xml) is relative to the directory where the template is saved. An absolute path also can be specified, for example:
mapping-schema="C:\MyDir\LimitFieldValue.xml"Create and use the SQLXML 4.0 Test Script (Sqlxml4test.vbs) to execute the template.
For more information, see Using ADO to Execute SQLXML Queries.
This is the result:
<ROOT xmlns:sql="urn:schemas-microsoft-com:xml-sql">
<Customer CustomerID="1" CompanyName="Company A">
<BillTo>Obere Str. 57 Berlin</BillTo>
<ShipTo>Avda. de la Constitución 2222 México D.F.</ShipTo>
</Customer>
<Customer CustomerID="2" CompanyName="Company B">
<BillTo>120 Hanover Sq., London</BillTo>
<ShipTo>Forsterstr. 57, Mannheim</ShipTo>
</Customer>
</ROOT>
B. Limiting results based on a discount value of type real data
In this example, a database contains two tables:
- Orders (OrderID)
- OrderDetails (OrderID, ProductID, UnitPrice, Quantity, Price, Discount)
This is the mapping schema in which the OrderID attribute on the order details maps to the OrderID column in the orders relation. The values that are returned for this attribute are limited to only those that have a value of 2.0000000e-001 (0.2) as specified for the Discount attribute using the sql:limit-field and sql:limit-value annotations.
This is the schema:
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:sql="urn:schemas-microsoft-com:mapping-schema">
<xsd:annotation>
<xsd:appinfo>
<sql:relationship name="OrderOrderDetails"
parent="Orders"
parent-key="OrderID"
child="OrderDetails"
child-key="OrderID" />
</xsd:appinfo>
</xsd:annotation>
<xsd:element name="root" sql:is-constant="1">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="Order" sql:relation="Orders" >
<xsd:complexType>
<xsd:sequence>
<xsd:element name="orderDetail"
sql:relation="OrderDetails"
sql:limit-field="Discount"
sql:limit-value="2.0000000e-001"
sql:relationship="OrderOrderDetails">
<xsd:complexType>
<xsd:attribute name="OrderID" />
<xsd:attribute name="ProductID" />
<xsd:attribute name="Discount" />
<xsd:attribute name="Quantity" />
<xsd:attribute name="UnitPrice" />
</xsd:complexType>
</xsd:element>
</xsd:sequence>
<xsd:attribute name="OrderID"/>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>
To test a sample XPath query against the schema
Create two tables in the tempdb database:
USE tempdb CREATE TABLE Orders ([OrderID] int NOT NULL ) ON [PRIMARY] ALTER TABLE Orders WITH NOCHECK ADD CONSTRAINT [PK_Orders] PRIMARY KEY CLUSTERED ( [OrderID] ) ON [PRIMARY] CREATE TABLE [OrderDetails] ( [OrderID] int NOT NULL , [ProductID] int NOT NULL , [UnitPrice] money NULL , [Quantity] smallint NOT NULL , [Discount] real NOT NULL ) ON [PRIMARY]Add the sample data:
INSERT INTO Orders ([OrderID]) values (10248) INSERT INTO Orders ([OrderID]) values (10250) INSERT INTO Orders ([OrderID]) values (10251) INSERT INTO Orders ([OrderID]) values (10257) INSERT INTO Orders ([OrderID]) values (10258) INSERT INTO [OrderDetails] ([OrderID],[ProductID],[UnitPrice],[Quantity],[Discount]) values (10248,11,14,12,0) INSERT INTO [OrderDetails] ([OrderID],[ProductID],[UnitPrice],[Quantity],[Discount]) values (10250,51,42.4,35,0.15) INSERT INTO [OrderDetails] ([OrderID],[ProductID],[UnitPrice],[Quantity],[Discount]) values (10251,22,16.8,6,0.05) INSERT INTO [OrderDetails] ([OrderID],[ProductID],[UnitPrice],[Quantity],[Discount]) values (10257,77,10.4,15,0) INSERT INTO [OrderDetails] ([OrderID],[ProductID],[UnitPrice],[Quantity],[Discount]) values (10258,2,15.2,50,0.2)Save the schema (LimitFieldValue.xml) in a directory.
Create the following test script (TestQuery.vbs), modify MyServer to the name of your SQL Server computer and save it in the same directory as you used in the previous step to save the schema:
Set conn = CreateObject("ADODB.Connection") conn.Open "Provider=SQLOLEDB;Data Source=MyServer;Database=tempdb;Integrated Security=SSPI" conn.Properties("SQLXML Version") = "sqlxml.4.0" Set cmd = CreateObject("ADODB.Command") Set stm = CreateObject("ADODB.Stream") Set cmd.ActiveConnection = conn stm.open result ="none" strXPathQuery="/root" DBGUID_XPATH = "{EC2A4293-E898-11D2-B1B7-00C04F680C56}" cmd.Dialect = DBGUID_XPATH cmd.CommandText = strXPathQuery cmd.Properties("Mapping schema") = "LimitFieldReal.xml" cmd.Properties("Output Stream").Value = stm cmd.Properties("Output Encoding") = "utf-8" WScript.Echo "executing for xml query" On Error Resume Next cmd.Execute , ,1024 if err then Wscript.Echo err.description Wscript.Echo err.Number Wscript.Echo err.source On Error GoTo 0 else stm.Position = 0 result = stm.ReadText end if WScript.Echo result Wscript.Echo "done"Execute the TestQuery.vbs file by clicking on it in Windows Explorer.
This is the result:
<root> <Order OrderID="10248"/> <Order OrderID="10250"/> <Order OrderID="10251"/> <Order OrderID="10257"/> <Order OrderID="10258"> <orderDetail OrderID="10258" ProductID="2" Discount="0.2" Quantity="50"/> </Order> </root>
Vedere anche
Riferimento
Using Annotated XSD Schemas in Queries (SQLXML 4.0)
Altre risorse
float e real (Transact-SQL)
nchar e nvarchar (Transact-SQL)
Deploying Applications with SQL Native Client