FME Transformers: 2025.2 BETA

Categories
Database

Database

Filters and Joins

Filters and Joins

Format Specific

Format Specific

Spatial Analysis

Spatial Analysis

Workflows

Workflows

Categories
Database

Database

Filters and Joins

Filters and Joins

Format Specific

Format Specific

Spatial Analysis

Spatial Analysis

Workflows

Workflows

FeatureReader

Reads features from any FME-supported format.

The features to be read are determined either by specifying feature types and optional constraints or, if the format supports it, by a custom query using the format’s query language.

When reading without a custom query, 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.

Optional Initiator Port

This transformer has two modes, depending on whether a connector is attached to the Initiator input port or not:

  • Input-driven: When input features are connected, the transformer runs once for each feature it receives in the Initiator port.
  • Run Once: When no input features are connected, the transformer runs one time.

When the Initiator input port is in use, the Initiator output port is also enabled.

Example

Configuration

Input Ports

This transformer accepts any feature.

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 and features that result from a custom query.

When input Initiator features are used, they are output here with a (_matched_records) attribute containing the number of features read for that 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.

Define Read Criteria By

For formats that support query languages like SQL and Cypher, there are two options for reading:

  • Constraint Parameters: Entire feature types will be read, subject to constraints defined below.
  • Custom Query: Arbitrary query statements will be executed against the dataset and the results will appear in the <Generic> output port.

Query

Only enabled if Custom Query was selected. Executes query statements against the database and returns resulting features through the <Generic> output port.

Constraints

Only enabled if Constraint Parameters was selected.

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"'.

Feature Type Order

Some formats that read multiple feature types also allow you to specify the order in which they are read. If it is available, the Select Feature Types to Read dialog (accessed via the ellipsis button) will have an additional Selected Items list that can be reordered.

Note  Older versions of the FeatureReader using colons as separators 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 Bounding Boxes 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 Initiator is OGC-Disjoint from Result 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.

Clip to Initiator Envelope

When enabled, read features are clipped to the 2D bounding box of the Initiator feature.

Clipping may be performed in conjunction with some Spatial Filter options including Initiator OGC-Intersects Result, Initiator OGC-Contains Result, Initiator OGC-Crosses Result, and Initiator OGC-Overlaps Result.

Clipping is done first, and the filter is applied to the clip results.

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.

Add Schema Attributes to Features

When enabled, attributes from schema features will be merged onto data features.

Use Cached Schemas

Schemas may be read for every dataset entering the reader. When:

  • Enabled (Default): One schema is read per feature type name, regardless of feature order.
  • Disabled: The schema is read on every dataset entering the reader.

Note that reading schemas on every dataset (disabled) can adversely affect performance in some scenarios.

Enable Data Feature Cache

The FeatureReader reads the source data every time an Initiator feature is received.

When enabled, Enable Cache creates a preprocessed cache to improve performance when rereading the data. Subsequent Initiator features or subsequent runs of the same workspace (on the same machine or engine) will use the contents of the cache.

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

Cache Timeout (hours)

Specify the length of time a cache will persist, in hours.

Note  The Cache Timeout value is a component of the cache. Different values correspond to different versions of the cached dataset. For example, if Cache Timeout is set to 1 hour and then reset to 2 hours on the same dataset, two cached copies could exist simultaneously.

Note that:

  • FeatureReader caches are not the same as FME Form's in-workspace data caching capability.
  • Using FeatureReader caches with FME Flow is not recommended and may behave unpredictably.
  • Caches are FME version and build-aware. If an FME instance with a different build number attempts to read the cache, it will be purged.

Output Order

Select an option for the ordering of output features:

  • <Default> - Use default feature ordering. The Initiator feature is output after read results.

  • Initiator First - Output the Initiator feature before the read results. Output Initiator features do not receive a _matched_records attribute .

Output Ports

Only enabled if Constraint Parameters was selected.

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 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

When input Initiator features are used for input-driven mode, select an attribute handling method:

  • 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

When input Initiator features are used for input-driven mode, select a geometry handling method:

  • 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

Transformer parameters can be set by directly entering values, using expressions, or referencing other elements in the workspace such as attribute values or user parameters. Various editors and context menus are available to assist. To see what is available, click beside the applicable parameter.

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.

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.

Table Tools

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.

For more information, see Transformer Parameter Menu Options.

Reference

Processing Behavior

Feature-Based

Feature Holding

No
Dependencies None
Aliases Querier OracleQuerier RasterReader
History  

FME Online Resources

The FME Community and Support Center Knowledge Base have a wealth of information, including active forums with 35,000+ members and thousands of articles.

Search for all results about the FeatureReader on the FME Community.

 

Examples may contain information licensed under the Open Government Licence – Vancouver, Open Government Licence - British Columbia, and/or Open Government Licence – Canada.