22.1 Comments/Troubleshooting
The
DataSet class provides a consistent programming
model, regardless of the actual data source. The
DataSet schema can be created programmatically,
read from a data source, read from an XML schema, or inferred from an
XML document or stream.
The DataSet serves as a container for disconnected
objects. It can contain DataTable objects in its
DataTableCollection and can be accessed through
its Tables property. These tables can be related
to one another using DataRelation objects in the
DataRelationCollection and are accessed through
the Relations property of the
DataSet. Data integrity can be maintained by
adding ForeignKeyConstraint and
UniqueConstraint objects to the
DataTable objects.
The data in the DataSet can be populated from the
data source, modified, and later reconciled back to a data source,
using a DataAdapter. Alternatively, the data can
be populated from XML documents or streams, modified, and saved as an
XML document or stream. Finally, the data stored in the
DataSet can be created and manipulated
programmatically.
The DataSet and XML are tightly coupled, which
permits the same data to be accessed and manipulated using either the
DataSet and its contained objects or by using
XML-based classes. This has two particularly important implications.
First, XSLT templates can easily be applied to any
DataSet to transform the data structure. Second,
the schema, data, or both the schema and data within a
DataSet can be persisted to memory or a file as an
XML document.
DataSets exist as both untyped and strongly typed.
Strongly typed DataSets are a collection of
automatically generated classes that inherit from the
DataSet, DataTable, and
DataRow classes and provide additional properties,
methods, and events based on the DataSet schema.
Strongly typed DataSets are discussed in detail in
Chapter 13.
The commonly used public properties of the DataSet
class are listed in Table 22-1.
Table 22-1. DataSet properties
CaseSensitive
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Gets or sets a value indicating whether string comparisons in the
DataSet are treated as case-sensitive.
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Locale
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Gets or sets the locale information that is the basis for string
comparisons in tables.
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DataSetName
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Gets or sets the name of the DataSet.
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EnforceConstraints
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Gets or sets a value indicating whether the constraint rules defined
between tables in the DataSet are enforced when
data is updated.
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HasErrors
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Gets a value indicating whether there are any errors in any rows
within any of the tables within the DataSet.
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Namespace
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Gets or sets the namespace of the DataSet.
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Prefix
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Gets or sets an XML prefix that aliases the namespace of the
DataSet.
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DefaultViewManager
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Gets a custom view of the data contained within the
DataSet for filtering, sorting, and navigating
using a DataViewManager.
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The commonly used public collections of the
DataSet class are listed in Table 22-2.
Table 22-2. DataSet collections
Tables
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Accesses the DataTableCollection that contains the
tables for the DataSet as a collection of
DataTable objects.
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Relations
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Accesses the DataRelationCollection that contains
table relationships for the DataSet as a
collection of DataRelation objects.
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ExtendedProperties
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Accesses the PropertyCollection that contains
custom information for the DataSet as a collection
of key-and-value pairs.
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The commonly used public methods of the DataSet
class are listed in Table 22-3.
Table 22-3. DataSet methods
AcceptChanges( )
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Commits all changes made to the DataSet since the
last time it was loaded or since the last time changes were
committed.
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Clear( )
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Removes all data rows from the DataSet.
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Clone( )
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Creates a new DataSet with the same schema as the
original but with none of the data.
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Copy( )
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Creates a new DataSet with the same schema and
data as the original.
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GetChanges( )
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Gets a copy of the changes made to a DataSet since
the last time it was loaded or since changes were last committed.
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GetXml( )
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Returns a string that is the XML representation of the data stored in
the DataSet, optionally with XSD schema
information.
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GetXmlSchema( )
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Returns a string that is the XSD schema for the XML representation of
the data stored in the DataSet.
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HasChanges( )
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Returns a value indicating whether data in the
DataSet has been modified, inserted, or deleted
since it was last loaded or since changes were last committed.
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InferXmlSchema( )
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Infers an XML schema from the contents of a specified
Stream, file, or TextReader
into the DataSet.
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Merge( )
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Merges data from another DataSet,
DataTable, or array of DataRows
into the DataSet.
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ReadXml( )
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Reads XML schema information and data from a
Stream, file, TextReader, or
XmlReader into the DataSet.
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ReadXmlSchema( )
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Reads XML schema information from a Stream, file,
TextReader, or XmlReader into
the DataSet.
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RejectChanges( )
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Rejects all changes made to the DataSet since the
last time it was loaded or since the last time changes were
committed.
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Reset( )
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Discards the contents of the DataSet, resetting it
to an uninitialized state.
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WriteXml( )
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Writes the data, and optionally the schema, from the
DataSet to a Stream, file,
TextReader, or XmlReader.
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WriteXmlSchema( )
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Writes the schema from the DataSet to a
Stream, file, TextReader, or
XmlReader.
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The commonly used public events of the DataSet
class are listed in Table 22-4.
Table 22-4. DataSet event
MergeFailed
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Raised when the schema of the source DataSet and
target DataSet being merged are in conflict.
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The DataSet class is contained within the
System.Data namespace. The
DataSet class inherits from
MarshalByValueComponent and implements the
IListSource,
ISupportInitialize, and
ISerializable interfaces. It is safe for
multithreaded read operations; multithreaded write operations must be
synchronized. DataSet objects can be passed
between different application domains.
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