Cinchoo ETL - FixedLength Writer

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5 Nov 2021CPOL23 min read

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Simple FixedLength file writer for .NET

ChoETL is an open source ETL (extract, transform and load) framework for .NET. It is a code based library for extracting data from multiple sources, transforming, and loading into your very own data warehouse in .NET environment. You can have data in your data warehouse in no time.

Introduction
Requirement
"Hello World!" Sample
1. Quick write - Data First Approach
2. Code First Approach
3. Configuration First Approach
Writing All Records
Write Records Manually
Customize FixedLength Record
Customize FixedLength Header
Customize FixedLength Fields
1. DefaultValue
2. ChoFallbackValue
3. Type Converters
4. Validations
Reserved
Callback Mechanism
1. BeginWrite
2. EndWrite
3. BeforeRecordWrite
4. AfterRecordWrite
5. RecordWriteError
6. BeforeRecordFieldWrite
7. AfterRecordFieldWrite
8. RecordWriteFieldError
Customization
Using Dynamic Object
Exceptions
Tips
Using MetadataType Annotation
Configuration Choices
1. Manual Configuration
2. Auto Map Configuration
3. Attaching MetadataType class
ToText Helper Method
Writing DataReader Helper Method
Writing DataTable Helper Method
Advanced Topics
1. Override Converters Format Specs
2. Currency Support
3. Enum Support
4. Boolean Support
5. DateTime Support

1. Introduction

This article talks about using FixedLengthRWriter component offered by ChoETL framework. It is a simple utility class to save FixedLength data to a file.

NOTE: Corresponding FixedLengthReader article can be found here.

Features

Follows FixedLength standard file rules. Gracefully handles data fields that contain commas and line breaks.
In addition to comma, most delimiting characters can be used, including tab delimited fields.
Supports culture specific date, currency and number formats while generating files.
Supports different character encoding.
Provides fine control of date, currency, enum, boolean, number formats when writing files.
Detailed and robust error handling, allowing you to quickly find and fix problems.
Shorten your development time.

2. Requirement

This framework library is written in C# using .NET 4.5 Framework.

3. "Hello World!" Sample

Open VS.NET 2013 or higher
Create a sample VS.NET (.NET Framework 4.5) Console Application project
Install ChoETL via Package Manager Console using Nuget Command: Install-Package ChoETL
Use the ChoETL namespace

Let's begin by looking into a simple example of generating the below FixedLength file having 2 columns.

Listing 3.1 Sample FixedLength data file (RecordLength: 18 chars)

Id      Name      
00000001Mark      
00000002Jason

There are a number of ways in which you can get the FixedLength file be created with minimal setup.

3.1. Quick Write - Data First Approach

This is the quick way to create FixedLength file in no time. No typed POCO object is needed. The sample code below shows how to generate the above sample FixedLength file using dynamic objects.

Listing 3.1.1 Write list of objects to FixedLength file

static void QuickWriteTest()
{
    List<ExpandoObject> objs = new List<ExpandoObject>();
    dynamic rec1 = new ExpandoObject();
    rec1.Id = 1;
    rec1.Name = "Mark";
    objs.Add(rec1);
 
    dynamic rec2 = new ExpandoObject();
    rec2.Id = 2;
    rec2.Name = "Jason";
    objs.Add(rec2);
 
    using (var parser = new ChoFixedLengthWriter("Emp.txt").
        WithField("Id", 0, 8. fieldType: typeof(int)).
        WithField("Name", 8, 10))
    {
        parser.Write(objs);
    }
}

In the above sample, define the individual column's start index and size using fluent API, then we give the list of objects to FixedLengthWriter at one pass to write them to FixedLength file.

Listing 3.1.2 Write each object to FixedLength file

static void QuickWriteTest2()
{
    using (var parser = new ChoFixedLengthWriter("Emp.txt").
        WithField("Id", 0, 8, fieldType: typeof(int)).
        WithField("Name", 8, 10))
    {
        dynamic rec1 = new ExpandoObject();
        rec1.Id = 1;
        rec1.Name = "Mark";
 
        parser.Write(rec1);
 
        dynamic rec2 = new ExpandoObject();
        rec2.Id = 2;
        rec2.Name = "Jason";
 
        parser.Write(rec2);
    }
}

In the above sample, we take control of constructing, passing each individual record to the FixedLengthWriter to generate the FixedLength file using Write overload.

3.2. Code First Approach

This is another way to generate FixedLength file using typed POCO class. First, define a simple POCO class to match the underlying FixedLength file layout.

Listing 3.2.1 Simple POCO entity class

public partial class EmployeeRecSimple
{
    public int Id { get; set; }
    public string Name { get; set; } 
}

In the above, the POCO class defines two properties matching the sample FixedLength file template.

Listing 3.2.2 Saving to FixedLength file

List<EmployeeRecSimple> objs = new List<EmployeeRecSimple>();

EmployeeRecSimple rec1 = new EmployeeRecSimple();
rec1.Id = 1;
rec1.Name = "Mark";
objs.Add(rec1);
 
EmployeeRecSimple rec2 = new EmployeeRecSimple();
rec2.Id = 2;
rec2.Name = "Jason";
objs.Add(rec2);
 
using (var parser = new ChoFixedLengthWriter<EmployeeRecSimple>("Emp.txt").
        WithField("Id", 0, 8, fieldType: typeof(int)).
        WithField("Name", 8, 10))
{
    parser.Write(objs);
}

The above sample shows how to create FixedLength file from typed POCO class objects.

3.3. Configuration First Approach

In this model, we define the FixedLength configuration with all the necessary parameters along with FixedLength columns required to generate the sample FixedLength file.

Listing 3.3.1 Define FixedLength configuration

ChoFixedLengthRecordConfiguration config = new ChoFixedLengthRecordConfiguration();
config.FixedLengthRecordFieldConfigurations.Add
(new ChoFixedLengthRecordFieldConfiguration("Id", 0, 8, fieldType: typeof(int)));
config.FixedLengthRecordFieldConfigurations.Add
(new ChoFixedLengthRecordFieldConfiguration("Name", 8, 10));

In the above, the class defines two FixedLength properties matching the sample FixedLength file template.

Listing 3.3.2 Generate FixedLength file without POCO object

List<ExpandoObject> objs = new List<ExpandoObject>();

dynamic rec1 = new ExpandoObject();
rec1.Id = 1;
rec1.Name = "Mark";
objs.Add(rec1);
 
dynamic rec2 = new ExpandoObject();
rec2.Id = 2;
rec2.Name = "Tom";
objs.Add(rec2);
 
using (var parser = new ChoFixedLengthWriter("Emp.txt", config))
{
    parser.Write(objs);
}

The above sample code shows how to generate FixedLength file from a list of dynamic objects using predefined FixedLength configuration setup. In the FixedLengthWriter constructor, we specified the FixedLength configuration object to obey the FixedLength layout schema while creating the file. If there is any mismatch in the name or count of FixedLength columns, it will be reported as an error and stops the writing process.

Listing 3.3.3 Saving FixedLength file with POCO object

List<EmployeeRecSimple> objs = new List<EmployeeRecSimple>();

EmployeeRecSimple rec1 = new EmployeeRecSimple();
rec1.Id = 1;
rec1.Name = "Mark";
objs.Add(rec1);
 
EmployeeRecSimple rec2 = new EmployeeRecSimple();
rec2.Id = 2;
rec2.Name = "Jason";
objs.Add(rec2);
 
using (var parser = new ChoFixedLengthWriter<EmployeeRecSimple>
("Emp.txt", config))
{
    parser.Write(objs);
}

The above sample code shows how to generate FixedLength file from a list of POCO objects with FixedLength configuration object. In the FixedLengthWriter constructor, we specified the FixedLength configuration configuration object.

3.4. Code First with Declarative Configuration

This is the combined approach to define POCO entity class along with attaching FixedLength configuration parameters declaratively. id is a required column and name is an optional value column with default value "XXXX". If name is not present, it will take the default value.

Listing 3.4.1 Define POCO Object

public class EmployeeRec
{
    [ChoFixedLengthRecordField(0, 8)]
    [Required]
    public int? Id
    {
        get;
        set;
    }

    [ChoFixedLengthRecordField(8, 10)]
    [DefaultValue("XXXX")]
    public string Name
    {
        get;
        set;
    }

    public override string ToString()
    {
        return "{0}. {1}.".FormatString(Id, Name);
    }
}

The code above illustrates about defining POCO object with necessary attributes required to generate FixedLength file. First thing defines property for each record field with ChoFixedLengthRecordFieldAttribute to qualify for FixedLength record mapping. Each property must specify StartIndex and Size of the field in order to be mapped to FixedLength column. StartIndex is 0 based. Id is a required property. We decorated it with RequiredAttribute. Name is given a default value using DefaultValueAttribute. It means that if the Name value is not set in the object, FixedLengthWriter uses the default value 'XXXX' to the file.

It is very simple and ready to save FixedLength data in no time.

Listing 3.4.2 Saving FixedLength file with POCO object

List<EmployeeRec> objs = new List<EmployeeRec>();

EmployeeRec rec1 = new EmployeeRec();
rec1.Id = 10;
rec1.Name = "Mark";
objs.Add(rec1);
 
EmployeeRec rec2 = new EmployeeRec();
rec2.Id = 200;
rec2.Name = "Lou";
objs.Add(rec2);
 
using (var parser = new ChoFixedLengthWriter<EmployeeRec>("Emp.txt"))
{
    parser.Write(objs);
}

We start by creating a new instance of ChoFixedLengthWriter object. That's all. All the heavy lifting of generating FixedLength data from the objects is done by the writer under the hood.

By default, FixedLengthWriter discovers and uses default configuration parameters while saving FixedLength file. These can be overridable according to your needs. The following sections will give you in-depth details about each configuration attribute.

4. Writing All Records

It is as easy as setting up POCO object match up with FixedLength file structure, construct the list of objects and pass it to FixedLengthWriter's Write method. This will write the entire list of objects into FixedLength file in one single call.

Listing 4.1 Write to FixedLength File

List<EmployeeRec> objs = new List<EmployeeRec>();
//Construct and attach objects to this list
...

using (var parser = new ChoFixedLengthWriter<EmployeeRec>("Emp.txt"))
{
    parser.Write(objs);
}

or:

Listing 4.2 Writer to FixedLength file stream

List<EmployeeRec> objs = new List<EmployeeRec>();
//Construct and attach objects to this list
...

using (var tx = File.OpenWrite("Emp.txt"))
{
    using (var parser = new ChoFixedLengthWriter<EmployeeRec>(tx))
    {
        parser.Write(objs);
    }
}

This model keeps your code elegant, clean, easy to read and maintain.

5. Write Records Manually

This is an alternative way to write each and individual record to FixedLength file in case when the POCO objects are constructed in a disconnected way.

Listing 5.1 Writing to FixedLength file

var writer = new ChoFixedLengthWriter<EmployeeRec>("Emp.txt");

EmployeeRec rec1 = new EmployeeRec();
rec1.Id = 10;
rec1.Name = "Mark";
 
writer.Write(rec1);

EmployeeRec rec2 = new EmployeeRec();
rec1.Id = 11;
rec1.Name = "Top"; 

writer.Write(rec2);

6. Customize FixedLength Record

Using ChoFixedLengthRecordObjectAttribute, you can customize the POCO entity object declaratively.

Listing 6.1 Customizing POCO object for each record

[ChoFixedLengthRecordObject(Encoding = "Encoding.UTF32", 
ErrorMode = ChoErrorMode.IgnoreAndContinue, IgnoreFieldValueMode = ChoIgnoreFieldValueMode.All)]
public class EmployeeRec
{
    [ChoFixedLengthRecordField(0, 8)]
    public int Id { get; set; }
    [ChoFixedLengthRecordField(8, 10, QuoteField = true)]
    [Required]
    [DefaultValue("ZZZ")]
    public string Name { get; set; }
}

Here are the available attributes to carry out customization of FixedLength load operation on a file:

EOLDelimiter - The value used to separate FixedLength rows. Default is \r\n (NewLine)
Culture - The culture info used to read and write
IgnoreEmptyLine - N/A
Comments - N/A
QuoteChar - The value used to escape fields that contain a delimiter, quote, or line ending
QuoteAllFields - A flag that tells the writer whether all fields written should have quotes around them; regardless of whether the field contains anything that should be escaped
Encoding - The encoding of the FixedLength file
HasExcelSeperator - N/A
ColumnCountStrict - This flag indicates if an exception should be thrown if FixedLength field configuration mismatch with the data object members
ColumnOrderStrict - N/A
BufferSize - The size of the internal buffer that is used when reader is from the StreamWriter
ErrorMode - This flag indicates if an exception should be thrown if writing and an expected field is failed to write. This can be overridden per property. Possible values are:
- IgnoreAndContinue - Ignore the error, record will be skipped and continue with next.
- ReportAndContinue - Report the error to POCO entity if it is of IChoNotifyRecordWrite type
- ThrowAndStop - Throw the error and stop the execution
IgnoreFieldValueMode - N/A
ObjectValidationMode - A flag to let the reader know about the type of validation to be performed with record object. Possible values are:
- Off - No object validation performed
- MemberLevel - Validation performed before each FixedLength property gets written to the file
- ObjectLevel - Validation performed before all the POCO properties are written to the file

7. Customize FixedLength Header

By attaching ChoFixedLengthFileHeaderAttribute to POCO entity object declaratively, you can influence the writer to generate FixedLength header when creating FixedLength file.

Listing 6.1 Customizing POCO object for file header

[ChoFixedLengthFileHeader]
public class EmployeeRec
{
    [ChoFixedLengthRecordField(0, 8)]
    public int Id { get; set; }
    [ChoFixedLengthRecordField(8, 10, QuoteField = true)]
    [Required]
    [DefaultValue("ZZZ")]
    public string Name { get; set; }
}

Here are the available members to add some customization to it according to your need.

FillChar - Padding character used when size of the FixedLength column header is short of the column size (ChoFixedLengthRecordFieldAttribute.Size or ChoFixedLengthRecordFieldConfiguration.Size). Default is '\0', padding will be off
Justification - Column header alignment. Default is Left
TrimOption - N/A
Truncate - This flag tells that the writer to truncate the FixedLength column header value if it is over the column size. Default is false

8. Customize FixedLength Fields

For each FixedLength column, you can specify the mapping in POCO entity property using ChoFixedLengthRecordFieldAttribute.

Listing 6.1 Customizing POCO Object for FixedLength Columns

[ChoFixedLengthFileHeader]
public class EmployeeRec
{
    [ChoFixedLengthRecordField(0, 8)]
    public int Id { get; set; }
    [ChoFixedLengthRecordField(8, 10, QuoteField = true)]
    [Required]
    [DefaultValue("ZZZ")]
    public string Name { get; set; }
}

Here are the available members to add some customization to it for each property:

StartIndex - The zero-based starting character position of a column in the line
FieldName - FixedLength Column name header. If not specified, POCO object property name will be used as column header
FillChar - Padding character used when size of the FixedLength column value is short of the column size. Default is '\0', padding will be off
FieldValueJustification - Column value alignment. Default is Left
FieldValueTrimOption - N/A
Truncate - This flag tells the writer to truncate the FixedLength column value if it is over the column size. Default is false
Size - Size of FixedLength column value
QuoteField - A flag that tells the writer that the FixedLength column value is surrounded by quotes.
ErrorMode - This flag indicates if an exception should be thrown if writing and an expected field failed to convert and write. Possible values are:
- IgnoreAndContinue - Ignore the error and continue to load other properties of the record
- ReportAndContinue - Report the error to POCO entity if it is of IChoRecord type
- ThrowAndStop - Throw the error and stop the execution
IgnoreFieldValueMode - N/A

8.1. DefaultValue

Any POCO entity property can be specified with default value using System.ComponentModel.DefaultValueAttribute. It is the value used to write when the FixedLength value is null (controlled via IgnoreFieldValueMode).

8.2. ChoFallbackValue

Any POCO entity property can be specified with fallback value using ChoETL.ChoFallbackValueAttribute. It is the value used and set to the property when the FixedLength value failed to convert as text. Fallback value only set when ErrorMode is either IgnoreAndContinue or ReportAndContinue.

8.3. Type Converters

Most of the primitive types are automatically converted to string/text and save them to FixedLength file. If the value of the FixedLength fields aren't automatically converted into the text value, you can specify a custom / built-in .NET converters to convert the value to text. These can be either IValueConverter or TypeConverter converters.

The methods to use to convert/format property values to text are IValueConverter.ConvertBack() or TypeConvert.ConvertTo().

Listing 8.3.1 Specifying type converters

[ChoFixedLengthFileHeader]
public class EmployeeRec
{
    [ChoFixedLengthRecordField(0, 8)]
    [ChoTypeConverter(typeof(IntConverter))]
    public int Id { get; set; }
    [ChoFixedLengthRecordField(8, 10, QuoteField = true)]
    [Required]
    [DefaultValue("ZZZ")]
    public string Name { get; set; }
}

Listing 8.3.2 IntConverter implementation

public class IntConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value;
    }
 
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        int intValue = (int)value;
        return intValue.ToString("D4");
    }
}

In the example above, we defined custom IntConverter class. And showed how to format 'Id' FixedLength property with leading zeros.

8.4. Validations

FixedLengthWriter leverages both System.ComponentModel.DataAnnotations and Validation Block validation attributes to specify validation rules for individual fields of POCO entity. Refer to the MSDN site for a list of available DataAnnotations validation attributes.

Listing 8.4.1 Using validation attributes in POCO entity

[ChoFixedLengthFileHeader]
[ChoFixedLengthRecordObject(Encoding = "Encoding.UTF32", ErrorMode = ChoErrorMode.IgnoreAndContinue,
       IgnoreFieldValueMode = ChoIgnoreFieldValueMode.All, ThrowAndStopOnMissingField = false)]
public partial class EmployeeRec
{
    [ChoFixedLengthRecordField(0, 8)]
    [ChoTypeConverter(typeof(IntConverter))]
    [Range(1, int.MaxValue, ErrorMessage = "Id must be > 0.")]
    [ChoFallbackValue(1)]
    public int Id { get; set; }
 
    [ChoFixedLengthRecordField(8, 10)]
    [Required]
    [DefaultValue("ZZZ")]
    [ChoFallbackValue("XXX")]
    public string Name { get; set; }
}

In the example above, used Range validation attribute for Id property. Required validation attribute to Name property. FixedLengthWriter performs validation on them before saving the data to file when Configuration.ObjectValidationMode is set to ChoObjectValidationMode.MemberLevel or ChoObjectValidationMode.ObjectLevel.

In some cases, you may want to take control and perform manual self validation within the POCO entity class. This can be achieved by inheriting POCO object from IChoValidatable interface.

Listing 8.4.2 Manual validation on POCO entity

[ChoFixedLengthFileHeader]
[ChoFixedLengthRecordObject
(Encoding = "Encoding.UTF32", ErrorMode = ChoErrorMode.IgnoreAndContinue,
       IgnoreFieldValueMode = ChoIgnoreFieldValueMode.All, ThrowAndStopOnMissingField = false)]
public partial class EmployeeRec : IChoValidatable
{
    [ChoFixedLengthRecordField(0, 8)]
    [ChoTypeConverter(typeof(IntConverter))]
    [Range(1, int.MaxValue, ErrorMessage = "Id must be > 0.")]
    [ChoFallbackValue(1)]
    public int Id { get; set; }
 
    [ChoFixedLengthRecordField(8, 10)]
    [Required]
    [DefaultValue("ZZZ")]
    [ChoFallbackValue("XXX")]
    public string Name { get; set; }
 
    public bool TryValidate
    (object target, ICollection<ValidationResult> validationResults)
    {
        return true;
    }
 
    public bool TryValidateFor
    (object target, string memberName, ICollection<ValidationResult> validationResults)
    {
        return true;
    }
 
    public void Validate(object target)
    {
    }
 
    public void ValidateFor(object target, string memberName)
    {
    }
}

The sample above shows how to implement custom self-validation in POCO object.

IChoValidatable interface exposes the below methods:

TryValidate - Validate entire object, return true if all validation passed. Otherwise, return false.
Validate - Validate entire object, throw exception if validation is not passed.
TryValidateFor - Validate specific property of the object, return true if all validation passed. Otherwise, return false.
ValidateFor - Validate specific property of the object, throw exception if validation is not passed.

10. Callback Mechanism

FixedLengthWriter offers industry standard FixedLength data file generation out of the box to handle most of the needs. If the generation process is not handling any of your needs, you can use the callback mechanism offered by FixedLengthWriter to handle such situations. In order to participate in the callback mechanism, Either POCO entity object or DataAnnotation's MetadataType type object must be inherited by IChoNotifyRecordWrite interface.

Tip: Any exceptions raised out of these interface methods will be ignored.

IChoNotifyRecordWrite exposes the below methods:

BeginWrite - Invoked at the begin of the FixedLength file write
EndWrite - Invoked at the end of the FixedLength file write
BeforeRecordWrite - Raised before the FixedLength record write
AfterRecordWrite - Raised after FixedLength record write
RecordWriteError - Raised when FixedLength record errors out while writing
BeforeRecordFieldWrite - Raised before FixedLength column value write
AfterRecordFieldWrite - Raised after FixedLength column value write
RecordFieldWriteError - Raised when FixedLength column value errors out while writing

Listing 10.1 Direct POCO callback mechanism implementation

[ChoFixedLengthFileHeader]
[ChoFixedLengthRecordObject
(Encoding = "Encoding.UTF32", ErrorMode = ChoErrorMode.IgnoreAndContinue,
       IgnoreFieldValueMode = ChoIgnoreFieldValueMode.All, ThrowAndStopOnMissingField = false)]
public partial class EmployeeRec : IChoNotifyrRecordWrite
{
    [ChoFixedLengthRecordField(0, 8)]
    [ChoTypeConverter(typeof(IntConverter))]
    [Range(1, int.MaxValue, ErrorMessage = "Id must be > 0.")]
    [ChoFallbackValue(1)]
    public int Id { get; set; }
    
    [ChoFixedLengthRecordField(8, 10, QuoteField = true)]
    [Required]
    [DefaultValue("ZZZ")]
    [ChoFallbackValue("XXX")]
    public string Name { get; set; }

    public bool AfterRecordFieldWrite(object target, int index, string propName, object value)
    {
        throw new NotImplementedException();
    }

    public bool AfterRecordWrite(object target, int index, object source)
    {
        throw new NotImplementedException();
    }

    public bool BeforeRecordFieldWrite(object target, int index, string propName, ref object value)
    {
        throw new NotImplementedException();
    }

    public bool BeforeRecordWrite(object target, int index, ref object source)
    {
        throw new NotImplementedException();
    }

    public bool BeginWrite(object source)
    {
        throw new NotImplementedException();
    }

    public void EndWrite(object source)
    {
        throw new NotImplementedException();
    }

    public bool RecordFieldWriteError
        (object target, int index, string propName, object value, Exception ex)
    {
        throw new NotImplementedException();
    }

    public bool RecordWriteError(object target, int index, object source, Exception ex)
    {
        throw new NotImplementedException();
    }
}

Listing 10.2 MetaDataType based callback mechanism implementation

[ChoFixedLengthFileHeader]
[ChoFixedLengthRecordObject
(Encoding = "Encoding.UTF32", ErrorMode = ChoErrorMode.IgnoreAndContinue,
       IgnoreFieldValueMode = ChoIgnoreFieldValueMode.All, ThrowAndStopOnMissingField = false)]
public class EmployeeRecMeta : IChoNotifyRecordWrite
{
    [ChoFixedLengthRecordField(0, 8)]
    [ChoTypeConverter(typeof(IntConverter))]
    [Range(1, int.MaxValue, ErrorMessage = "Id must be > 0.")]
    [ChoFallbackValue(1)]
    public int Id { get; set; }

    [ChoFixedLengthRecordField(8. 10, QuoteField = true)]
    [Required]
    [DefaultValue("ZZZ")]
    [ChoFallbackValue("XXX")]
    public string Name { get; set; }
 
    public bool AfterRecordFieldWrite(object target, int index, string propName, object value)
    {
        throw new NotImplementedException();
    }

    public bool AfterRecordWrite(object target, int index, object source)
    {
        throw new NotImplementedException();
    }

    public bool BeforeRecordFieldWrite(object target, int index, string propName, ref object value)
    {
        throw new NotImplementedException();
    }

    public bool BeforeRecordWrite(object target, int index, ref object source)
    {
        throw new NotImplementedException();
    }

    public bool BeginWrite(object source)
    {
        throw new NotImplementedException();
    }

    public void EndWrite(object source)
    {
        throw new NotImplementedException();
    }

    public bool RecordFieldWriteError
       (object target, int index, string propName, object value, Exception ex)
    {
        throw new NotImplementedException();
    }

    public bool RecordWriteError(object target, int index, object source, Exception ex)
    {
        throw new NotImplementedException();
    }
} 

[MetadataType(typeof(EmployeeRecMeta))]
public partial class EmployeeRec
{
    [ChoFixedLengthRecordField(0, 8)]
    [ChoTypeConverter(typeof(IntConverter))]
    [Range(1, int.MaxValue, ErrorMessage = "Id must be > 0.")]
    [ChoFallbackValue(1)]
    public int Id { get; set; }
    
    [ChoFixedLengthRecordField(8, 10, QuoteField = true)]
    [Required]
    [DefaultValue("ZZZ")]
    [ChoFallbackValue("XXX")]
    public string Name { get; set; }
}

10.1 BeginWrite

This callback invoked once at the beginning of the FixedLength file write. source is the FixedLength file stream object. In here, you have a chance to inspect the stream, return true to continue the FixedLength generation. Return false to stop the generation.

Listing 10.1.1 BeginWrite Callback Sample

public bool BeginWrite(object source)
{
    StreamReader sr = source as StreamReader;
    return true;
}

10.2 EndWrite

This callback invoked once at the end of the FixedLength file generation. source is the FixedLength file stream object. In here, you have a chance to inspect the stream, do any post steps to be performed on the stream.

Listing 10.2.1 EndWrite Callback Sample

public void EndWrite(object source)
{
    StreamReader sr = source as StreamReader;
}

10.3 BeforeRecordWrite

This callback invoked before each POCO record object is written to FixedLength file. target is the instance of the POCO record object. index is the line index in the file. source is the FixedLength record line. In here, you have a chance to inspect the POCO object, and generate the FixedLength record line if needed.

Tip: If you want to skip the record from writing, set the source to null.

Tip: If you want to take control of FixedLength record line generation, set the source to valid FixedLength record line text.