Programming Portal: REAL TIME QUESTOINS ADO.NET PART ONE

Explain what a diffgram is and its usage ?

A DiffGram is an XML format that is used to identify current and original versions of data elements. The DataSet uses the DiffGram format to load and persist its contents, and to serialize its contents for transport across a network connection.

When a DataSet is written as a DiffGram, it populates the DiffGram with all the necessary information to accurately recreate the contents, though not the schema, of the DataSet, including column values from both the Original and Current row versions, row error information, and row order.

When sending and retrieving a DataSet from an XML Web service, the DiffGram format is implicitly used. Additionally, when loading the contents of a DataSet from XML using the ReadXml method, or when writing the contents of a DataSet in XML using the WriteXml method, you can select that the contents be read or written as a DiffGram.

The DiffGram format consists of the following blocks of data:

The name of this element, DataInstance, is used for explanation purposes in this documentation. A DataInstance element represents a DataSet or a row of a DataTable. Instead of DataInstance, the element would contain the name of the DataSet or DataTable. This block of the DiffGram format contains the current data, whether it has been modified or not. An element, or row, that has been modified is identified with the diffgr:hasChanges annotation.

This block of the DiffGram format contains the original version of a row. Elements in this block are matched to elements in the DataInstance block using the diffgr:id annotation.

This block of the DiffGram format contains error information for a particular row in the DataInstance block. Elements in this block are matched to elements in the DataInstance block using the diffgr:id annotation.

Which method do you invoke on the DataAdapter control to load your generated dataset with data?

You have to use the Fill method of the DataAdapter control and pass the dataset object as an argument to load the generated data.

Which are the different IsolationLevels ?

• Serialized Data read by a current transaction cannot be changed by another transaction until the current transaction finishes. No new data can be inserted that would affect the current transaction. This is the safest isolation level and is the default.
• Repeatable Read Data read by a current transaction cannot be changed by another transaction until the current transaction finishes. Any type of new data can be inserted during a transaction.
• Read Committed A transaction cannot read data that is being modified by another transaction that has not committed. This is the default isolation level in Microsoft® SQL Server.
• Read Uncommitted A transaction can read any data, even if it is being modified by another transaction. This is the least safe isolation level but allows the highest concurrency.
• Any Any isolation level is supported. This setting is most commonly used by downstream components to avoid conflicts. This setting is useful because any downstream component must be configured with an isolation level that is equal to or less than the isolation level of its immediate upstream component.

Therefore, a downstream component that has its isolation level configured as Any always uses the same isolation level that its immediate upstream component uses. If the root object in a transaction has its isolation level configured to Any, its isolation level becomes Serialized.

How xml files and be read and write using dataset?

DataSet exposes method like ReadXml and WriteXml to read and write xml.

What are the different rowversions available?

There are four types of Rowversions.

Current:

The current values for the row. This row version does not exist for rows with a RowState of Deleted.

Default :

The row the default version for the current DataRowState. For a DataRowState value of Added, Modified or Current, the default version is Current. For a DataRowState of Deleted, the version is Original. For a DataRowState value of Detached, the version is Proposed.

Original:

The row contains its original values.

Proposed:

The proposed values for the row. This row version exists during an edit operation on a row, or for a row that is not part of a DataRowCollection

Explain acid properties?

The term ACID conveys the role transactions play in mission-critical applications. Coined by transaction processing pioneers, ACID stands for atomicity, consistency, isolation, and durability.

These properties ensure predictable behavior, reinforcing the role of transactions as all-or-none propositions designed to reduce the management load when there are many variables.

Atomicity

A transaction is a unit of work in which a series of operations occur between the BEGIN TRANSACTION and END TRANSACTION statements of an application. A transaction executes exactly once and is atomic — all the work is done or none of it is.
Operations associated with a transaction usually share a common intent and are interdependent. By performing only a subset of these operations, the system could compromise the overall intent of the transaction. Atomicity eliminates the chance of processing a subset of operations.

Consistency

A transaction is a unit of integrity because it preserves the consistency of data, transforming one consistent state of data into another consistent state of data.

Consistency requires that data bound by a transaction be semantically preserved. Some of the responsibility for maintaining consistency falls to the application developer who must make sure that all known integrity constraints are enforced by the application. For example, in developing an application that transfers money, you should avoid arbitrarily moving decimal points during the transfer.

Isolation

A transaction is a unit of isolation — allowing concurrent transactions to behave as though each were the only transaction running in the system.

Isolation requires that each transaction appear to be the only transaction manipulating the data store, even though other transactions may be running at the same time. A transaction should never see the intermediate stages of another transaction.

Transactions attain the highest level of isolation when they are serializable. At this level, the results obtained from a set of concurrent transactions are identical to the results obtained by running each transaction serially. Because a high degree of isolation can limit the number of concurrent transactions, some applications reduce the isolation level in exchange for better throughput.

Durability

A transaction is also a unit of recovery. If a transaction succeeds, the system guarantees that its updates will persist, even if the computer crashes immediately after the commit. Specialized logging allows the system's restart procedure to complete unfinished operations, making the transaction durable.

Whate are different types of Commands available with DataAdapter ?

The SqlDataAdapter has

SelectCommand,
InsertCommand,
DeleteCommand and
UpdateCommand

What is a Dataset?

Datasets are the result of bringing together ADO and XML. A dataset contains one or more data of tabular XML, known as DataTables, these data can be treated separately, or can have relationships defined between them. Indeed these relationships give you ADO data SHAPING without needing to master the SHAPE language, which many people are not comfortable with.

DataTableCollection:

As we say that a DataSet is an in-memory database. So it has this collection, which holds data from multiple tables in a single DataSet object.
DataTable: In the DataTableCollection, we have DataTable objects, which represents the individual tables of the dataset.

DataView:

The way we have views in database, same way we can have DataViews. We can use these DataViews to do Sort, filter data.

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