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replace value of (XML DML)

Updates the value of a node in the document.


replace value of 
      Expression1 
with
      Expression2
Expression1

Identifies a node whose value is to be updated. It must identify only a single node. That is, Expression1 must be a statical singleton. If the XML is typed, the type of the node must be a simple type. If multiple nodes are selected, an error is raised. If Expression1 returns an empty sequence, no value replacement occurs and no errors are returned. Expression1 must return a single element that has simply typed content (list or atomic types), a text node, or an attribute node. Expression1 cannot be a union type, a complex type, a processing instruction, a document node, or a comment node. If it is, an error is returned.

Expression2

Identifies the new value of the node. This can be an expression that returns a simply typed node, because data() will be used implicitly. If the value is a list of values, the update statement replaces the old value with the list. In modifying a typed XML instance, Expression2 must be the same type or a subtype of Expression1. Otherwise, an error is returned. In modifying an untyped XML instance, Expression2 must be an expression that can be atomized. Otherwise, an error is returned.

The following examples of the replace value of XML DML statement illustrates how to update nodes in an XML document.

A. Replacing values in an XML instance

In the following example, a document instance is first assigned to a variable of xml type. Then, replace value of XML DML statements update values in the document.

DECLARE @myDoc xml
SET @myDoc = '<Root>
<Location LocationID="10" 
            LaborHours="1.1"
            MachineHours=".2" >Manufacturing steps are described here.
<step>Manufacturing step 1 at this work center</step>
<step>Manufacturing step 2 at this work center</step>
</Location>
</Root>'
SELECT @myDoc

-- update text in the first manufacturing step
SET @myDoc.modify('
  replace value of (/Root/Location/step[1]/text())[1]
  with     "new text describing the manu step"
')
SELECT @myDoc
-- update attribute value
SET @myDoc.modify('
  replace value of (/Root/Location/@LaborHours)[1]
  with     "100.0"
')
SELECT @myDoc

Note that the target being updated must be, at most, one node that is explicitly specified in the path expression by adding a "[1]" at the end of the expression.

B. Using the if expression to determine replacement value

You can specify the if expression in Expression2 of the replace value of XML DML statement, as shown in the following example. Expression1 identifies that the LaborHours attribute from the first work center is to be updated. Expression2 uses an if expression to determine the new value of the LaborHours attribute.

DECLARE @myDoc xml
SET @myDoc = '<Root>
<Location LocationID="10" 
            LaborHours=".1"
            MachineHours=".2" >Manu steps are described here.
<step>Manufacturing step 1 at this work center</step>
<step>Manufacturing step 2 at this work center</step>
</Location>
</Root>'
--SELECT @myDoc

SET @myDoc.modify('
  replace value of (/Root/Location[1]/@LaborHours)[1]
  with (
       if (count(/Root/Location[1]/step) > 3) then
         "3.0"
       else
          "1.0"
      )
')
SELECT @myDoc

C. Updating XML stored in an untyped XML column

The following example updates XML stored in a column:

drop table T
go
CREATE TABLE T (i int, x xml)
go
INSERT INTO T VALUES(1,'<Root>
<ProductDescription ProductID="1" ProductName="Road Bike">
<Features>
  <Warranty>1 year parts and labor</Warranty>
  <Maintenance>3 year parts and labor extended maintenance is available</Maintenance>
</Features>
</ProductDescription>
</Root>')
go
-- verify the current <ProductDescription> element
SELECT x.query(' /Root/ProductDescription')
FROM T
-- update the ProductName attribute value
UPDATE T
SET x.modify('
  replace value of (/Root/ProductDescription/@ProductName)[1]
  with "New Road Bike" ')
-- verify the update
SELECT x.query(' /Root/ProductDescription')
FROM T

D. Updating XML stored in a typed XML column

This example replaces values in a manufacturing instructions document stored in a typed XML column.

In the example, you first create a table (T) with a typed XML column in the AdventureWorks database. You then copy a manufacturing instructions XML instance from the Instructions column in the ProductModel table into table T. Insertions are then applied to XML in table T.

use AdventureWorks
go
drop table T
go
create table T(ProductModelID int primary key, 
Instructions xml (Production.ManuInstructionsSchemaCollection))
go
insert  T 
select ProductModelID, Instructions
from Production.ProductModel
where ProductModelID=7
go
--insert a new location - <Location 1000/>. 
update T
set Instructions.modify('
  declare namespace MI="http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelManuInstructions";
insert <MI:Location LocationID="1000"  LaborHours="1000"  LotSize="1000" >
           <MI:step>Do something using <MI:tool>hammer</MI:tool></MI:step>
         </MI:Location>
  as first
  into   (/MI:root)[1]
')
go
select Instructions
from T
go
-- Now replace manu. tool in location 1000
update T
set Instructions.modify('
  declare namespace MI="http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelManuInstructions";
  replace value of (/MI:root/MI:Location/MI:step/MI:tool)[1] 
  with   "screwdriver"
')
go
select Instructions
from T
-- Now replace value of lot size
update T
set Instructions.modify('
  declare namespace MI="http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelManuInstructions";
  replace value of (/MI:root/MI:Location/@LotSize)[1] 
  with   500 cast as xs:decimal ?
')
go
select Instructions
from T

Note the use of cast when replacing LotSize value. This is required when the value must be of a specific type. In this example, if 500 were the value, explicit casting would not be necessary.

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