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How do you fix there is already an open DataReader associated with this Command which must be closed first?
You can use the ToList() method before the return statement.
How do you check if a DataReader is closed or opened in C#?
using (SqlDataReader rdr = MySqlCommandObject. ExecuteReader()) { while (rdr. Read()) { // } } // The SqlDataReader is guaranteed to be closed here, even if an exception was thrown. This is the way we do it as well.
How do I turn off data reader?
You should always call the Close method when you have finished using the DataReader object.The following code example iterates through a DataReader object, and returns two columns from each row. while (myReader.Read()) Console. WriteLine(“\t{0}\t{1}”, myReader. GetInt32(0), myReader. GetString(1)); myReader. Close();.
What is DataReader in VB net?
DataReader is a readonly, forward only and connected recordset from the database. In DataReader, database connection is opened until the object is closed unlike DataSet. Using DataReader we can able to access one row at a time so there it is not required storing it in memory.
What is DataReader object?
In ADO.NET, a DataReader is a broad category of objects used to sequentially read data from a data source. DataReaders provide a very efficient way to access data, and can be thought of as a Firehose cursor from ASP Classic, except that no server-side cursor is used.
What is DataReader in asp net?
The DataReader is the solution for forward streaming data through ADO.NET. The data reader is also called a firehose cursor or forward read-only cursor because it moves forward through the data.
Does closing DataReader close connection?
1) Yes, DataReader. Close() will close the connection. This is relevant when dealing with any connected object.
What is DataSet and DataReader?
Dataset is used to hold tables with data. DataReader is designed to retrieve a read-only, forward-only stream of data from data sources. DataReader has a connection oriented nature, whenever you want fetch the data from database that you must have a connection.
Do I need to close SqlDataReader?
You must ensure the Close method is called when you are through using the SqlDataReader before using the associated SqlConnection for any other purpose. Do not call Close or Dispose on a Connection, a DataReader, or any other managed object in the Finalize method of your class.
Which is faster DataReader or DataAdapter?
Using a DataReader produces faster results than using a DataAdapter to return the same data. Because the DataAdapter actually uses a DataReader to retrieve data, this should not surprise us.
What is SQL DataReader?
SqlDataReader Object provides a connection oriented data access to the SQL Server data Sources from C# applications. When the ExecuteReader method in the SqlCommand Object execute , it will instantiate a SqlClient.
Can DataReader have multiple tables?
Answers. It IS possible to handle multiple result sets with a reader. string sqlText = “Select this, that from here; select somethingelse from there”; Jul 7, 2008.
What is DataReader and DataAdapter?
DataAdapter is an intermediate layer/ middleware which acts a bridge between the DataSet and a Database whereas DataReader provides forward-only, read-only access to data using a server-side cursor (simply put it is ued to read the data).
How does DataReader work in C#?
The data reader reads a record at a time, but it reads it from the underlying database driver. The database driver reads data from the database in blocks, typically using a buffer that is 8 kilobytes.
Is the main method of DataReader?
To create a SqlDataReader instance, we must call the ExecuteReader method of the SqlCommand object.Methods. Method Description Close() It is used to closes the SqlDataReader object. GetBoolean(Int32) It is used to get the value of the specified column as a Boolean.
How do I use DataReader in Python?
Working with Pandas Datareader using Python import pandas as pd import pandas_datareader.data as web import matplotlib.pyplot as plt. start_date = “2020-01-1” end_date = “2020-12-31″ data = web.DataReader(name=”TSLA”, data_source=’yahoo’, start=start_date, end=end_date) print(data).
Why do we use SqlDataReader?
The ADO.NET SqlDataReader class in C# is used to read data from the SQL Server database in the most efficient manner. It reads data in the forward-only direction. It means, once it read a record, it will then read the next record, there is no way to go back and read the previous record. SqlDataReader is read-only.
Which of the following types of cursors is available with ADO Net DataReader object *?
ADO supports four types of cursors: static, forward-only, keyset, and dynamic.
How can we force the connection object to close after my DataReader is closed?
How can we force the connection object to close after my datareader is closed ? user using() to free the memory allocated for resource . We can use “CommandBehaviour. CloseConnection” Like as :SqlCommand cmd = new SqlCommand(“SELECT * FROM EMPLOYEE”, con);con.
How do I close a data reader in VB net?
3 Answers. The best way is to use the Using -statement which ensures that unmanaged resources are disposed(even on error). This also closes the reader.
Does ExecuteReader close connection?
Ultimately it is the Close method of the data reader that will close the connection, provided nothing has gone wrong before. If there is an exception that occurs inside ExecuteReader or any of its called methods, before the actual DataReader object is constructed, then no, the connection will not be closed.
When would you choose a DataSet or DataReader?
A critical choice when designing your application is whether to use a DataSet or a DataReader. If you need to retrieve many records rapidly, use a DataReader. The DataReader object is fast, returning a fire hose of read-only data from the server, one record at a time.
How do I use a DataAdapter?
The DataAdapter works as a bridge between a DataSet and a data source to retrieve data. DataAdapter is a class that represents a set of SQL commands and a database connection. It can be used to fill the DataSet and update the data source.
What is difference between SqlDataReader and SqlDataAdapter?
A SqlDataAdapter is typically used to fill a DataSet or DataTable and so you will have access to the data after your connection has been closed (disconnected access). The SqlDataReader is a fast forward-only and connected cursor which tends to be generally quicker than filling a DataSet/DataTable.
What is CommandBehavior CloseConnection?
ExecuteReader(CommandBehavior. CloseConnection); The associated connection will be closed automatically when the Close method of the Datareader is called. This makes it all the more important to always remember to call Close on your datareaders.
Does using statement close SQL connection?
The using statement handles the disposal and subsequent closing of my objects for me. For objects like the SqlConnection, this also closes the connection too.
