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DataTypeAttribute Class

Specifies the name of an additional type to associate with a data field.

Namespace:  System.ComponentModel.DataAnnotations
Assemblies:   System.ComponentModel.Annotations (in System.ComponentModel.Annotations.dll)
  System.ComponentModel.DataAnnotations (in System.ComponentModel.DataAnnotations.dll)

[AttributeUsageAttribute(AttributeTargets.Method|AttributeTargets.Property|AttributeTargets.Field|AttributeTargets.Parameter, AllowMultiple = false)]
public class DataTypeAttribute : ValidationAttribute

The DataTypeAttribute type exposes the following members.

  NameDescription
Public methodSupported by Portable Class LibraryDataTypeAttribute(DataType)Initializes a new instance of the DataTypeTypeAttribute class by using the specified type name.
Public methodSupported by Portable Class LibraryDataTypeAttribute(String)Initializes a new instance of the DataTypeTypeAttribute class by using the specified field template name.
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  NameDescription
Public propertySupported by Portable Class LibraryCustomDataTypeGets the name of custom field template that is associated with the data field.
Public propertySupported by Portable Class LibraryDataTypeGets the type that is associated with the data field.
Public propertySupported by Portable Class LibraryDisplayFormatGets a data-field display format.
Public propertySupported by Portable Class LibraryErrorMessageGets or sets an error message to associate with a validation control if validation fails. (Inherited from ValidationAttribute.)
Public propertySupported by Portable Class LibraryErrorMessageResourceNameGets or sets the error message resource name to use in order to look up the ErrorMessageResourceType property value if validation fails. (Inherited from ValidationAttribute.)
Public propertySupported by Portable Class LibraryErrorMessageResourceTypeGets or sets the resource type to use for error-message lookup if validation fails. (Inherited from ValidationAttribute.)
Protected propertySupported by Portable Class LibraryErrorMessageStringGets the localized validation error message. (Inherited from ValidationAttribute.)
Public propertyRequiresValidationContextGets a value that indicates whether the attribute requires validation context. (Inherited from ValidationAttribute.)
Public propertyTypeIdWhen implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute.)
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  NameDescription
Public methodSupported by Portable Class LibraryEqualsInfrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
Protected methodSupported by Portable Class LibraryFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodSupported by Portable Class LibraryFormatErrorMessageApplies formatting to an error message, based on the data field where the error occurred. (Inherited from ValidationAttribute.)
Public methodSupported by Portable Class LibraryGetDataTypeNameReturns the name of the type that is associated with the data field.
Public methodSupported by Portable Class LibraryGetHashCodeReturns the hash code for this instance. (Inherited from Attribute.)
Public methodSupported by Portable Class LibraryGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodSupported by Portable Class LibraryGetValidationResultChecks whether the specified value is valid with respect to the current validation attribute. (Inherited from ValidationAttribute.)
Public methodIsDefaultAttributeWhen overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute.)
Public methodIsValid(Object)Checks that the value of the data field is valid. (Overrides ValidationAttribute.IsValid(Object).)
Protected methodSupported by Portable Class LibraryIsValid(Object, ValidationContext)Validates the specified value with respect to the current validation attribute. (Inherited from ValidationAttribute.)
Public methodMatchWhen overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
Protected methodSupported by Portable Class LibraryMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodSupported by Portable Class LibraryToStringReturns a string that represents the current object. (Inherited from Object.)
Public methodSupported by Portable Class LibraryValidate(Object, ValidationContext)Validates the specified object. (Inherited from ValidationAttribute.)
Public methodValidate(Object, String)Validates the specified object. (Inherited from ValidationAttribute.)
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  NameDescription
Explicit interface implemetationPrivate method_Attribute.GetIDsOfNamesMaps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.GetTypeInfoRetrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.GetTypeInfoCountRetrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.InvokeProvides access to properties and methods exposed by an object. (Inherited from Attribute.)
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The DataTypeAttribute attribute enables you to mark fields by using a type that is more specific than the database intrinsic type. The type name is selected from the DataType enumeration type. For example, a string data field that contains e-mail addresses can be specified as the EmailAddress type. This information is then accessed by the field templates to modify how the data field is processed.

You use the DataTypeAttribute attribute for the following reasons:

  • To provide additional type information for a data field. You do this by applying the DataTypeAttribute attribute to a data field in the data model and by specifying the additional type name from the DataType enumeration. The field template that processes the data field can access this additional metadata type information to determine how to process the field. For example, the text field template can generate hyperlinks for e-mail addresses whose intrinsic type is String.

  • To associate a custom field template with a data field. The specified custom field template will then be used to process the data field. This is an alternative to using the UIHintAttribute attribute.

When you apply the DataTypeAttribute attribute to a data field you must do the following:

  • Follow the attribute usage rules.

  • Implement the metadata class that contains the data fields to which you want to apply the attribute.

  • Issue validation errors as appropriate.

For more information, see ASP.NET Dynamic Data Guidelines.

See a run-time code example of this feature: Run.

The following example uses the DataTypeAttribute attribute to customize the display of the EmailAddress data field. The e-mail addresses are shown as hyperlinks instead of as simple text, which is what Dynamic Data would infer from the intrinsic data type. The example code is in three parts, and it performs the following steps:

  • It implements a metadata partial class and the associated metadata class.

  • In the associated metadata class, it applies the DataTypeAttribute attribute to the EmailAddress data field by specifying the EmailAddress enumerated value. This indicates to the Text.ascx field template that it should customize the display of e-mail addresses.

  • It modifies the Text.ascx field template to customize the display of the EmailAddress data fields.

using System;
using System.Web.DynamicData;
using System.ComponentModel.DataAnnotations;


[MetadataType(typeof(CustomerMetaData))]
public partial class Customer
{


}

public class CustomerMetaData
{

    // Add type information.
    [DataType(DataType.EmailAddress)]
    public object EmailAddress;

}

<%@ Control Language="C#" 
CodeFile="Text.ascx.cs" Inherits="TextField" %>

<!-- Removed, evaluated in the code behind.
<%# FieldValueString %> --> 
using System;
using System.Linq;
using System.Web.UI.WebControls;
using System.Web.DynamicData;
using System.ComponentModel.DataAnnotations;

public partial class TextField : 
    System.Web.DynamicData.FieldTemplateUserControl {

    protected override void OnDataBinding(EventArgs e)
    {
        base.OnDataBinding(e);
        bool processed = false;
        var metadata = MetadataAttributes.OfType
            <DataTypeAttribute>().FirstOrDefault();
        if (metadata != null)
        {
            if (metadata.DataType == DataType.EmailAddress)
            {
                if (!string.IsNullOrEmpty(FieldValueString))
                {
                    processed = true;
                    HyperLink hyperlink = new HyperLink();
                    hyperlink.Text = FieldValueString;
                    hyperlink.NavigateUrl = "mailto:" + FieldValueString;
                    Controls.Add(hyperlink);
                }
            }
        }
        if (!processed)
        {
            Literal literal = new Literal();
            literal.Text = FieldValueString;
            Controls.Add(literal);
        }
    }

}

To compile and run the example code, you need the following:

  • Visual Studio 2008 Service Pack 1 or Visual Developer 2008 Express Edition Service Pack 1.

  • The AdventureWorksLT sample database. For information about how to download and install the SQL Server sample database, see Microsoft SQL Server Product Samples: Database on the CodePlex site. Make sure that you install the correct version of the sample database for the version of SQL Server that you are running (SQL Server 2005 or SQL Server 2008).

  • A data-driven Web site. This enables you to create a data context for the database and to create the class that contains the data field to customize. For more information, see Walkthrough: Creating a New Dynamic Data Web Site using Scaffolding.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5 SP1

.NET Framework Client Profile

Supported in: 4

Portable Class Library

Supported in: Portable Class Library

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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