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Professional binary robot review
By default, the DataReader loads incoming data as a row as soon as an entire row of data is available. Binary large objects BLOBs need different treatment, however, because they can contain gigabytes of data that cannot be contained in a single row. ExecuteReader method has an overload that will take a CommandBehavior argument to modify the default behavior of the DataReader. You can pass SequentialAccess to the ExecuteReader method to modify the default behavior of the DataReader so that instead of loading rows of data, it will load data sequentially as it is received.
This is ideal for loading BLOBs or other large data structures. Note that this behavior may depend on your data source. When setting the DataReader to use SequentialAccess , it is important to note the sequence in which you access the fields returned. The default behavior of the DataReader , which loads an entire row as soon as it is available, allows you to access the fields returned in any order until the next row is read. When using SequentialAccess however, you must access the fields returned by the DataReader in order.
For example, if your query returns three columns, the third of which is a BLOB, you must return the values of the first and second fields before accessing the BLOB data in the third field. If you access the third field before the first or second fields, the first and second field values are no longer available.
This is because SequentialAccess has modified the DataReader to return data in sequence and the data is not available after the DataReader has read past it. You can also use GetString for character data; however. You can instead specify a specific buffer size of data to be returned, and a starting location for the first byte or character to be read from the returned data. GetBytes and GetChars will return a long value, which represents the number of bytes or characters returned.
You can optionally specify an index in the array as a starting position for the data being read. Because the logo field is a bitmap, the example returns binary data using GetBytes. Notice that the publisher ID is accessed for the current row of data before the logo, because the fields must be accessed sequentially.
The feedback system for this content will be changing soon. Old comments will not be carried over. If content within a comment thread is important to you, please save a copy. For more information on the upcoming change, we invite you to read our blog post. SequentialAccess Do While reader. Read ' Get the publisher id, which must occur before getting the logo. GetString 0 ' Create a file to hold the output. GetBytes 1, startIndex, outByte, 0, bufferSize ' Continue while there are bytes beyond the size of the buffer.
Flush ' Reposition start index to end of the last buffer and fill buffer. Write outByte, 0 , retval - 1 writer. Flush ' Close the output file. Close Loop ' Close the reader and the connection. SequentialAccess ; while reader. Write outByte ; writer.
Write outByte, 0, int retval ; writer.