FeatureReader

Categories

Filters and Joins

Format Specific

Spatial Analysis

Workflows

Reads features from any FME-supported format.

A complete read is done for each feature that enters the Initiator port. The features resulting from the read are output either through named output ports or through the generic output port.

The features read can be constrained by specifying a WHERE clause or a spatial filter for formats that support them. Most reader settings and constraints can be configured dynamically from attribute values on the input features.

Additionally, a schema feature representing the feature type definition is output for each encountered feature type. The schema features can be used to configure feature type definitions for dynamic writing.

Example

Configuration

Input Ports

Receives features that initiate feature reading.

Output Ports

Output port for schema features. If connected, a schema feature is produced for each unique feature type encountered during read. The schema feature is guaranteed to be output before any data features of the same feature type and is output only once per translation.

Note that schema features receive a new attribute fme_schema_handling with the value schema only. This attribute is used in writers to indicate that the feature should be used to define a schema only and then discarded, and so care should be taken if subsequently merging with other features.

Schema reading may affect performance. If the schema feature output port is not connected or Features to Read is set to Data Features, then schema reading will not occur and there will be no performance penalty. If a list of feature types to read was specified then schema reading will stop as soon as schemas for all the listed feature types have been output. If no feature types to read were listed, then schema reading will occur on every Initiator feature.

Performance can be improved when only reading schemas by configuring the transformer to not read data features. This is done by setting Features to Read to Schema Features or by ensuring that the <Generic>, the <Initiator>, and the named feature type output ports are not connected.

Parameters for Constraints or for Attribute and Geometry Handling do not apply to schema features.

Generic output port for features that do not have a corresponding named output port.

Upon read success, outputs the original Initiator features with the addition of the _matched_records attributes which holds the number of data features read for that Initiator feature.

Upon reader error, outputs the original Initiator feature with the addition of the _reader_error attribute which contains the last error message from the reader.

Note: <Rejected> features are accessible only if the workspace is run with feature inspection, or if the <Generic> or <Initiator> port connects to another transformer (such as a Junction).

Output Ports can be optionally generated for all or a subset of the feature types available to read.

Parameters

Reader

Select the Reader format and dataset, including any reader-specific parameters.

Constraints

Feature Types to Read

Enter the feature types that will be read. Feature types can be selected from a list generated by the reader by clicking the Browse button. For some formats, the parameter can be left empty to indicate all feature types should be read.

When published, this parameter can be represented as a fixed list, a fixed list with aliases, or left as a dynamic list that determines the feature types at runtime.

Feature types can also come from an existing attribute or generated from an expression. To specify the feature types, separate each feature type with a space. If a feature type name contains a space or a double quote, then quote the whole feature type name with double quotes and escape any internal double quotes with an additional double quote. For example, a feature type named 'my "special" table' would become '"my ""special"" table"'.

Note: Older versions of the FeatureReader using colon as a separator will work as before, but can be updated (see Feature Type Separator).

Feature Type Separator

This option allows older versions of the FeatureReader to change the separator for multiple feature types in an attribute to be a space instead of a colon. The colon separator is deprecated; once space has been selected, colon cannot be re-selected.

This option is only available to versions 4 and older of the FeatureReader that had been upgraded to version 5 or newer and that were specifying feature types to read from an attribute.

WHERE Clause

For formats that support it, only features that fulfill the WHERE clause will be read.

A WHERE clause is used to filter the results and takes the form:

column_name operator value

FME attributes can be used to substitute values in the WHERE clause using the syntax

@Value(<attribute>)

For example, "ID" = @Value(road_id)

User Parameters can be used to substitute values in the WHERE clause with the syntax

$(User Parameter)

For example, "PATHID" =$(ROAD_DID)

Spatial Filter

Select only features that fulfill the specified spatial relationship with the Initiator feature. See Spatial Relations Defined for a description of the permitted spatial relations. Select <No Spatial Filter> when no spatial filtering is desired. Select Envelope OGC-Intersects to read only those features whose envelope intersects the Initiator feature’s envelope.

The performance of the Spatial Filter can vary depending on the spatial filter being applied and whether the reader supports a Spatial Index. Spatial Filtering is done in two steps: first the candidate features are read, then the more costly filter is applied. For readers that support a Spatial Index, the candidate features are fetched by performing a search envelope on the reader which can greatly improve performance as not all features are read. For readers that do not support a Spatial Index or when the relationship OGC-Disjoint is selected, all features are considered candidate features and so all features are read. Check the format’s Quick Facts section to see if the reader supports a Spatial Index.

Note that when setting the Spatial Filter from an attribute, the attribute value can be any of the options found in the drop down list.

Max Features to Read

Limits the number of data features on each read. If left empty or set to a number less than one, all features are read.

Schema/Data Features

Features to Read

Schema and Data Features: Schema features and data features are read and output based on whether their corresponding output ports are connected. For data features, this includes the <Initiator>, <Generic>, and named feature type output ports. For schema features, it is the <Schema> output port.

Schema Features: Only schema features are read and output. Data features are not read.

Data Features: Only data features are read and output. Schema features are not read.

Enable Cache

Cache Timeout

By default, this transformer rereads the original source data for each Initiator feature. To improve performance (for example, with web services, databases, or URLs), you can choose to create a preprocessed cache to improve speed when rereading the original source data.

The cache expires after the specified time interval, or if the original data file is modified.

Note: The Cache Timeout value is also a component of the preprocessed cache. This means that different values of Cache Timeout correspond to different versions of the cached dataset. For example, if the FeatureReader is set with a Cache Timeout of 1 hour, then set a second time with the same dataset, but with a Cache Timeout of 2 hours, there will be two cached copies of this dataset.

Output Ports

Output Ports

Output ports can be optionally generated for all or a subset of the feature types available to read. Features that do not have a generated output port will exit the generic output port. In order for output ports to be generated, the reader must be fully specified and accessible.

One per Feature Type

An output port is generated for each feature type to read.

Ports will be regenerated when any Reader parameters are changed, and will also be regenerated if the Regenerate checkbox is enabled.

Single Output Port

No additional output ports are generated. All feature types will exit out of the generic output port.

Specified

Enter a list of feature types that will be used to generate the output ports. Feature types can also be selected from a list generated by the reader by clicking the Browse button.

Regenerate

When Output Ports is set to One per Feature Type or Specified, output ports may be regenerated on exiting the parameters dialog with OK. Select a regeneration frequency:

  • Always

  • On Reader Parameter Change

  • Never

Accumulation Mode

Merge Initiator and Result: Output features will contain all of the un-conflicted attributes from the results of the read as well as any un-conflicted attributes from the Initiator feature. This mode will handle conflicted attributes based on the Conflict Resolution parameter.

Only Use Result: Output features will contain only attributes resulting from the read.

Only Use Initiator: Output features will contain all of the attributes from the Initiator feature, but none of the attributes resulting from the read.

Prefix Initiator: Output features will contain attributes resulting from the read, as well as attributes from the Initiator feature but with the Initiator attribute names prefixed with the Prefix parameter.

Conflict Resolution

Use Result: If a conflict occurs, the values resulting from the read will be used.

Use Initiator: If a conflict occurs, the values of the Initiator will be used.

Ignore Nulls

Enabled when Accumulation Mode is set to Merge Initiator and Result.

If Yes, where there are attributes with the same name on both Initiator and Result feature, if one has a value of <null> then the other attribute value will be used.

If No, the Conflict Resolution selection will be strictly observed, including keeping null values.

Prefix

If the Accumulation Mode parameter is set to Prefix Initiator, this value will prefix attributes from the Initiator feature.

Geometry

Result: The feature geometry from the results of the read is used.

Initiator: The feature geometry from the Initiator feature is used.

Aggregate Initiator and Result: The feature geometry is an aggregate of the geometry from the Initiator feature followed by the geometry from the result of the read. The aggregate geometry will be tagged with the coordinate system from the result of the read. The Initiator geometry will not be reprojected. This can create unexpected results if it is in a different coordinate system. For best results, ensure the Initiator geometry has the same coordinate system as the geometry being read.

 

<Generic> Port

Attributes to Expose

Enter the names of attributes to expose on the <Generic> output port. The attributes will be ordered in the same sequence as specified in the list.

Editing Transformer Parameters

Using a set of menu options, transformer parameters can be assigned by referencing other elements in the workspace. More advanced functions, such as an advanced editor and an arithmetic editor, are also available in some transformers. To access a menu of these options, click beside the applicable parameter. For more information, see Transformer Parameter Menu Options.

Defining Values

There are several ways to define a value for use in a Transformer. The simplest is to simply type in a value or string, which can include functions of various types such as attribute references, math and string functions, and workspace parameters. There are a number of tools and shortcuts that can assist in constructing values, generally available from the drop-down context menu adjacent to the value field.

Using the Text Editor

The Text Editor provides a convenient way to construct text strings (including regular expressions) from various data sources, such as attributes, parameters, and constants, where the result is used directly inside a parameter.

Text Editor

Using the Arithmetic Editor

The Arithmetic Editor provides a convenient way to construct math expressions from various data sources, such as attributes, parameters, and feature functions, where the result is used directly inside a parameter.

Arithmetic Editor

Conditional Values

Set values depending on one or more test conditions that either pass or fail.

Parameter Condition Definition Dialog

Content

Expressions and strings can include a number of functions, characters, parameters, and more.

When setting values - whether entered directly in a parameter or constructed using one of the editors - strings and expressions containing String, Math, Date/Time or FME Feature Functions will have those functions evaluated. Therefore, the names of these functions (in the form @<function_name>) should not be used as literal string values.

String Functions

These functions manipulate and format strings.

Special Characters

 A set of control characters is available in the Text Editor.

Math Functions

Math functions are available in both editors.
Date/Time Functions Date and time functions are available in the Text Editor.

Math Operators

These operators are available in the Arithmetic Editor.

FME Feature Functions

These return primarily feature-specific values.

FME Parameters

FME and workspace-specific parameters may be used.
Creating and Modifying User Parameters Create your own editable parameters.

Dialog Options - Tables

Transformers with table-style parameters have additional tools for populating and manipulating values.

Row Reordering

Enabled once you have clicked on a row item. Choices include:

  • Add a row
  • Remove a row
  • Move current row up one
  • Move current row down one
  • Move current row to top
  • Move current row to bottom

Cut, Copy, and Paste

Enabled once you have clicked on a row item. Choices include:

  • Cut a row - delete and copy to clipboard
  • Copy a row to the clipboard
  • Paste a row from the clipboard

Cut, copy, and paste may be used within a transformer, or between transformers.

Filter

Start typing a string, and the matrix will only display rows matching those characters. Searches all columns. This only affects the display of attributes within the transformer - it does not alter which attributes are output.

Import

Import populates the table with a set of new attributes read from a dataset. Specific application varies between transformers.

Reset/Refresh

Generally resets the table to its initial state, and may provide additional options to remove invalid entries. Behavior varies between transformers.

Note: Not all tools are available in all transformers.

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