Some Readers allow to read data from the optional input port.

Input port reading is supported by the following Readers:

	Important
	Remember that port reading can also be used by DBExecute for receiving SQL commands. Query URL will be as follows: port:$0.fieldName:discrete. Also SQL command can be read from a file. Its name, including path, is then passed to DBExecute from input port and the Query URL attribute should be the following: port:$0.fieldName:source.

If you connect the optional input port of any of these Readers to an edge, you must also connect the other side of this edge to some data source. To define the protocol for field mapping, a field from where you want to read data must be set in the File URL attribute of the Reader. The type of the FieldName input field can only be string, byte, or cbyte as defined in input edge metadata.

The protocol has the syntax port:$0.FieldName[:processingType].

Here processingType is optional and defines if the data is processed as plain data or url addresses. It can be source, discrete, or stream. If not set explicitly, discrete is applied by default.

To define the attributes of input port reading, URL File Dialog can be used.

When graph runs, data is read from the original data source (according to the metadata of the edge connected to the optional input port of the Readers) and received by the Reader through its optional input port. Each record is read independently of the other records. The specified field of each one is processed by the Reader according to the output metadata.