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How a Data Source Control Creates

Parameters for Data-bound Fields

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When you use a data-bound control such as a

GridView, DetailsView, or FormView control with

an ASP.NET data source control, the data-

bound control can pass parameter names andvalues to the data source control based on the

bound fields in the data-bound control.

The data source control then includes the

field names and values in the parameter

collection for select or update operations.

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Dictionaries Passed to Data Source

Controls

When a data-bound control requests an operation

from the data source control, it passes one or more

IDictionary collections containing parameter names

and values for the requested data operation. The values of the name/value pairs in the dictionary

are derived from child controls. For example, in an

update operation, the data-bound control reads

parameter values from TextBox or CheckBox

controls that are displayed in edit mode.

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The names for the name/value pairs are taken from

the names of the fields bound to child controls and

from the field names specified in the DataKeyNames

property.

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Name/value pairs are passed using the following

IDictionary collections :

Values collection Passed for an insert operation.Contains the name/value pairs for a new record. Field

names and values for the Values collection are taken

from child controls in an InsertItemTemplate or from

bound fields in a DetailsView control Keys collection Passed for update and delete

operations. Contains the primary key or keys for

the record being updated or deleted.

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NewValues collection Passed for an updateoperation. Contains the name/value pairs withnew values for the updated item, including newvalues for updatable key fields. Field names andvalues for the NewValues collection are takenfrom child controls in an EditItemTemplate orfrom bound fields in a DetailsView controlwhose ReadOnly property is set to false.

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OldValues collection Passed for update or deleteoperations. Contains the original values for the datarecord to use for optimistic concurrency checking.

When a data-bound control is populated with data fromthe data source control, it maintains that data in viewstate. When an update or delete operation is requested,the OldValues collection is populated with values storedearlier in view state. If the data-bound control's

EnableViewState property is set to false, theOldValues collection is not populated for the update ordelete operation.

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Parameter Names

The data source control creates parameters

automatically for the values passed in the

IDictionary collections. For an insert operation, the

data source control populates its InsertParameters

collection with values from the name/value pairs inthe Values collection.

For an update operation, the data source control

populates its UpdateParameters collection with

values from the name/value pairs in the Keys,NewValues, and OldValues collections.

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For a delete operation, the data source control

populates its DeleteParameters collection

with values from the name/value pairs in the

Keys and OldValues collections.

The OldValues collection is not populated by

default. It is populated only when the data-

source control's ConflictDetectionproperty isset to CompareAllValues.

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If you need to access both current and original bound

values, such as a scenario where you must support

optimistic concurrency checks, you can have the datasource control create parameters for both current and

original values.

To do this, you must establish a naming convention for

parameters that will contain original values. The formatof the parameters for original values is determined by the

OldValuesParameterFormatString property.

Set the OldValuesParameterFormatString property toa string that includes "{0}" as a placeholder for the name

of the field.

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Consider an update operation that involves a

field named LastModifiedDate. The current

value for the field is passed in the Values

dictionary and the original value for the field is

passed in the OldValues dictionary. A

parameter named @LastModifiedDate is

created to pass the current value and aparameter named @old_LastModifiedDate is

created to pass the original value.

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If a data-bound control such as a GridView control isbound to the SqlDataSource control, during an updateor delete operation the data-bound control passes bothcurrent and original record values to theSqlDataSource control.

The current values are passed in the Valuesdictionary. The original values are passed in the Keysor OldValues dictionaries. The contents of thesedictionaries are appended to the underlyingDbCommand object's Parameters collection for agiven data operation.

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DbCommand Class

Represents an SQL statement or stored

procedure to execute against a data

source. Provides a base class for

database-specific classes that representcommands.

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DbCommand.Parameters Property

Gets the collection ofDbParameter

objects.

http://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref4/html/T_System_Data_Common_DbParameter.htmhttp://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref4/html/T_System_Data_Common_DbParameter.htm

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SqlDataSource.ConflictDetection Property

The ConflictDetection property determines

whether parameters for old and new values are

applied to the Update method.

If the ConflictDetection property is set to theCompareAllValues value, parameters are

created for Name, Number, original_Name, and

original_Number. (The exact name of the

parameters for the original values depends onthe OldValuesParameterFormatString property.)

http://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/P_System_Web_UI_WebControls_SqlDataSource_OldValuesParameterFormatString.htmhttp://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/P_System_Web_UI_WebControls_SqlDataSource_OldValuesParameterFormatString.htm

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By setting the ConflictDetection property to the

CompareAllValues value, your Update method can

then compare the old and new values to the original

data source to detect conflicts and handle them, asnecessary

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ConflictOptions Enumeration :

CompareAllValuesA data source control uses the

oldValues collection of the Update and Delete

methods to determine whether the data has beenchanged by another process.

OverwriteChangesA data source control overwritesall values in a data row with its own values for the

row.

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CompareAllValues

If the data source control is configured touse the CompareAllValues option,however, the control passes the original

data in the oldValues collections of theUpdate and Delete methods so that youcan write logic to update or delete dataonly if these values match the values

currently in the data storage. Thematching values indicate that the data hasnot changed since the time it was read.

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OverwriteChanges

By default, the ConflictDetection property

is set to OverwriteChanges, which means

the data source control will overwrite any

changes made to a data row between thetime the data source control first read data

from the row and the time that the row is

updated.

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Parameter Class

The Parameterclass represents a parameter in

a parameterized SQL query, a filtering

expression, or a business object method call that

an ASP.NET data source control uses to select,filter, or modify data.

Parameterobjects are contained in a

ParameterCollection object

http://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/T_System_Web_UI_WebControls_ParameterCollection.htmhttp://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/T_System_Web_UI_WebControls_ParameterCollection.htm

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Use the parameter classes that are provided

with ASP.NET, including ControlParameter,

CookieParameter, SessionParameter,

ProfileParameter, and QueryStringParameter,with data source and data-bound controls to

build Web-based data applications. These

classes are used by data source controls to bind

specific kinds of values found in Webapplications to placeholders in SQL query

strings,

http://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/T_System_Web_UI_WebControls_ControlParameter.htmhttp://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/T_System_Web_UI_WebControls_CookieParameter.htmhttp://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/T_System_Web_UI_WebControls_SessionParameter.htmhttp://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/T_System_Web_UI_WebControls_ProfileParameter.htmhttp://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/T_System_Web_UI_WebControls_QueryStringParameter.htmhttp://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/T_System_Web_UI_WebControls_QueryStringParameter.htmhttp://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/T_System_Web_UI_WebControls_ProfileParameter.htmhttp://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/T_System_Web_UI_WebControls_SessionParameter.htmhttp://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/T_System_Web_UI_WebControls_CookieParameter.htmhttp://ms-help//MS.VSCC.v80/MS.MSDN.v80/MS.NETDEVFX.v20.en/cpref16/html/T_System_Web_UI_WebControls_ControlParameter.htm

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Data source controls typically include a

parameter collection for each data

operation. When selecting data, you can

specify a SelectParameters collection,when updating a data item you can specify

an UpdateParameters collection