- [Instructor] We have spent most of this section
exploring LINQ to Entities,
but there is another LINQ variation worth mentioning,
LINQ to DataSet.
We'll cover it briefly in this chapter.
If you are familiar with LINQ to Objects,
transitioning to LINQ to DataSet is a natural step
when working with in-memory relational data in ADO.NET.
Unlike LINQ to Entities,
LINQ to DataSet doesn't involve data models,
DB context, or navigation properties.
Instead, it's designed for scenarios
where you're working with older ADO.NET classes,
like DataSet and DataTable.
If you have data stored in these classes
and want to apply LINQ queries to filter,
sort, or transform it,
LINQ to DataSet provides the tools to do this.
ADO.NET is a library that provides powerful tools
for connecting to databases, retrieving data,
and managing it in memory using classes,
like DataSet and DataTable.
ADO.NET predates LINQ and Entity Framework.
That doesn't make it insignificant, though.
It provides a wealth of data services.
It supports connected
and disconnected modes of data access,
data interaction, data caching, and CRUD operations.
Also, after local data modifications,
ADO.NET ensures those changes are synchronized
back to the database.
A DataSet is essentially
an in-memory representation of a database.
Once the DataSet is filled with data,
it can be disconnected from the.
Now we can manipulate the data locally,
all without requiring an active database connection.
This disconnected nature makes ADO.NET highly efficient
for scenarios where frequent database access
is impractical or unnecessary.
A DataTable is an in-memory representation
of a single database table,
consisting of rows and columns,
and provides methods for filtering,
sorting, and managing those records.
A DataSet is a container
that holds a collection of DataTables.
Each DataTable contains columns
that define the structure of the table,
specifying data types and constraints.
Rows hold the actual data records.
A primary key in a DataTable ensures
that each row has a unique identifier,
just like in a relational database.
Constraints in a DataTable help enforce data integrity
by restricting how data can be entered or modified.
When multiple DataTables exist within a DataSet,
we can create data relations
to define parent-child relationships.
These relationships allow navigation
between related records in different tables.
DataAdapters act as a bridge between a DataSet
and the database,
enabling data retrieval and updates.
Since the DataSet operates in a disconnected manner,
it needs a DataAdapter to fetch data from the database
and later send those changes back.
A DataAdapter uses commands,
such as SELECT, INSERT, UPDATE, and DELETE,
to interact with the database,
and it relies on a connection object
to establish communication.
This isn't a course on ADO.NET,
so we won't go too deep into the topic.
However, it's important to recognize
there are valid scenarios
where data might be stored in DataTables and DataSets.
When that happens, we can still leverage LINQ to DataSet
to query and manipulate the data.
The core of LINQ to DataSet revolves
around a single method called AsEnumberable.
This method enables us to treat the rows of a DataTable
as an IEnumerable,
making them compatible with LINQ operations.
Since LINQ to Objects works with any IEnumerable,
calling AsEnumberable effectively moves us
into the LINQ to Objects territory.
This means we can use LINQ queries
just as we would with collections,
like lists or arrays.
In LINQ to DataSets,
the query results return a collection of DataRows.
Since each row represents a record in the DataSet,
we will be working with properties
and methods on the DataRow class to access
or manipulate the data.
LINQ to DataSet is a valuable tool for querying
and manipulating in-memory data,
especially in applications that still rely on DataSets
and haven't fully transitioned to Entity Framework.
It provides a modern, readable way
to work with a collection of DataRows.