Cinchoo ETL - YAML Reader

Cinchoo

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1 Jul 2020CPOL34 min read

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Simple YAML reader 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 load - Data First Approach
2. Code First Approach
3. Configuration First Approach
4. Code First with declarative configuration
Reading All Records
Read Records Manually
Customize YAML Record
Customize YAML Fields
1. DefaultValue
2. ChoFallbackValue
3. Type Converters
  1. Declarative Approach
  2. Configuration Approach
4. Validations
Callback Mechanism
1. Using ChoYamlReader events
2. Implementing IChoNotifyRecordRead interface
3. BeginLoad
4. EndLoad
5. BeforeRecordLoad
6. AfterRecordLoad
7. RecordLoadError
8. BeforeRecordFieldLoad
9. AfterRecordFieldLoad
10. RecordLoadFieldError
11. SkipUntil
12. DoWhile
Customization
AsDataReader Helper Method
AsDataTable Helper Method
Using Dynamic Object
1. DefaultValue
2. ChoFallbackValue
3. FieldType
4. Type Converters
5. Validations
Working with sealed POCO object
Exceptions
Using MetadataType Annotation
Configuration Choices
1. Manual Configuration
2. Auto Map Configuration
3. Attaching MetadataType class
LoadText Helper Method
Advanced Topics
1. Override Converters Format Specs
2. Currency Support
3. Enum Support
4. Boolean Support
5. DateTime Support
Fluent API
1. WithYamlPath
2. WithFields
3. WithField
4. ColumnCountStrict
5. NotifyAfter
6. Configure
7. Setup
FAQs
1. How to deserialize string as enum?
2. How to load only the values from Key-Value Pair YAML?
3. How to load only the keys from Key-Value Pair YAML?
4. Deserialize YAML into dynamic object?
5. How to convert YAML to XML?
6. How to load selective nodes from YAML?
7. How to load selective subnodes from YAML?
8. How to convert YAML to DataTable?
9. How to convert YAML to DataReader?
10. How to convert YAML to CSV?
11. How to deserialize an object?
12. How to deserialize a collection?
13. How to deserialize a Dictionary?
14. How to deserialize from a file?
15. How to deserialize with custom factory?
16. Reading an entire file - Using a simple data structure
17. Reading an entire file - Using Multiple Lists
18. Using generic data structures (IDictionnary)
19. Using generic data lists (IList)
20. Reading an entire file - Dynamic structures
History

1. Introduction

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.

YAML is a human-readable data serialization standard that can be used in conjunction with all programming languages and is often used to write configuration files.

This article talks about using ChoYamlReader component offered by ChoETL framework. It is a simple utility class to extract YAML data from file / source to objects.

Features

Uses SharpYaml parser under the hood, parses YAML file in seconds and also handles large file without any memory issues
Stream based parsers allow for ultimate performance, low resource usage, and nearly unlimited versatility scalable to any size data file, even tens or hundreds of gigabytes
Event based data manipulation and validation allows total control over the flow of data during the bulk insert process
Exposes IEnumarable list of objects - which is often used with LINQ query for projection, aggregation and filtration, etc.
Supports deferred reading
Supports processing files with culture specific date, currency and number formats
Recognizes a wide variety of date, currency, enum, boolean and number formats when reading files
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 the problems

2. Requirement

This framework library is written in C# using .NET 4.5 Framework / .NET Core 2.x.

3. "Hello World!" Sample

Open VS.NET 2017 or higher
Create a sample VS.NET (.NET Framework 4.5 / .NET Core 2.x) Console Application project
Install ChoETL via Package Manager Console using Nuget Command based on the .NET environment:
- Install-Package ChoETL.Yaml
Use the ChoETL namespace

Let's begin by looking into a simple example of reading YAML file having three fields.

Listing 3.1 Sample YAML data file (emp.yaml)

YAML

emps:
    - id: 1
      name: Tom

    - id: 2
      name: Mark

There are a number of ways in which you can get the YAML file parsing started with minimal setup.

3.1. Quick load - Data First Approach

It is the zero config, quick way to load a YAML file in no time. No POCO object is required. The sample code below shows how to load the file.

Listing 3.1.1 Load YAML File using Iterator

foreach (dynamic e in new ChoYamlReader("emp.yaml")
                .WithYamlPath("$.emps[*]"))
{
    Console.WriteLine(e.Id);
    Console.WriteLine(e.Name);
}

Listing 3.1.2 Load YAML File using Loop

var reader = new ChoYamlReader("emp.yaml").WithYamlPath("$.emps[*]");
dynamic rec;
 
while ((rec = reader.Read()) != null)
{
    Console.WriteLine(e.Id);
    Console.WriteLine(e.Name);
}

3.2. Code First Approach

This is another zero config way to parse and load YAML file using POCO class. First, define a simple data class to match the underlying YAML file layout.

Listing 3.2.1 Simple POCO Entity Class

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

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

Listing 3.2.2 Load YAML File

foreach (var e in new ChoYamlReader<EmployeeRec>("emp.yaml").WithYamlPath("$.emps[*]"))
{
    Console.WriteLine(e.Id);
    Console.WriteLine(e.Name);
}

3.3. Configuration First Approach

In this model, we define the YAML configuration with all the necessary parsing parameters along with yaml fields matching with the underlying YAML file.

Listing 3.3.1 Define YAML Configuration

ChoYamlRecordConfiguration config = new ChoYamlRecordConfiguration();
config.YamlRecordFieldConfigurations.Add(new ChoYamlRecordFieldConfiguration("Id"));
config.YamlRecordFieldConfigurations.Add(new ChoYamlRecordFieldConfiguration("Name"));

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

Listing 3.3.2 Load YAML File without POCO Object

foreach (dynamic e in new ChoYamlReader("emp.yaml", config).WithYamlPath("$.emps[*]"))
{
    Console.WriteLine(e.Id);
    Console.WriteLine(e.Name);
}

Listing 3.3.3 Load YAML File with POCO Object

foreach (var e in new ChoYamlReader<EmployeeRec>
        ("emp.yaml", config).WithYamlPath("$.emps[*]"))
{
    Console.WriteLine(e.Id);
    Console.WriteLine(e.Name);
}

3.4. Code First with Declarative Configuration

This is the combined approach to define POCO entity class along with YAML configuration parameters decorated declaratively. Id is required field and Name is optional value field 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
{
    [ChoYamlRecordField]
    [Required]
    public int Id
    {
        get;
        set;
    }
    [ChoYamlRecordField]
    [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 to carry the values of each record line in the input file. First thing defines property for each record field with ChoYamlRecordFieldAttribute to qualify for YAML record mapping. YamlPath is an optional property. If not specified, framework automatically discovers and loads the values from yaml property. Id is decorated with RequiredAttribute, if the value is missing, it will throw an exception. Name is given default value using DefaultValueAttribute. It means that if the Name yaml field contains empty value in the file, it will be defaulted to 'XXXX' value.

It is very simple and ready to extract YAML data in no time.

Listing 3.4.2 Main Method

foreach (var e in new ChoYamlReader<EmployeeRec>("emp.yaml").WithYamlPath("$.emps[*]"))
{
    Console.WriteLine(e.Id);
    Console.WriteLine(e.Name);
}

We start by creating a new instance of ChoYamlReader object. That's all. All the heavy lifting of parsing and loading YAML data stream into the objects is done by the parser under the hood.

By default, ChoYamlReader discovers and uses default configuration parameters while loading YAML file. These can be overridable according to your needs. The following sections will give details about each configuration attribute.

4. Reading All Records

It is as easy as setting up POCO object match up with YAML file structure, you can read the whole file as enumerable pattern. It is a deferred execution mode, but take care while making any aggregate operation on them. This will load the entire file records into memory.

Listing 4.1 Read YAML File

foreach (var e in new ChoYamlReader<EmployeeRec>("emp.yaml").WithYamlPath("$.emps[*]"))
{
    Console.WriteLine(e.Id);
    Console.WriteLine(e.Name);
}

or:

Listing 4.2 Read YAML File Stream

foreach (var e in new ChoYamlReader<EmployeeRec>(textReader).WithYamlPath("$.emps[*]"))
{
    Console.WriteLine(e.Id);
    Console.WriteLine(e.Name);
}

This model keeps your code elegant, clean, easy to read and maintain. It also leverages LINQ extension methods to perform grouping, joining, projection, aggregation, etc.

Listing 4.3 Using LINQ

var list = (from o in new ChoYamlReader<EmployeeRec>("emp.yaml").WithYamlPath("$.emps[*]")
           where o.Name != null && o.Name.StartsWith("R")
           select o).ToArray();
 
foreach (var e in list)
{
    Console.WriteLine(e.Id);
    Console.WriteLine(e.Name);
}

5. Read Records Manually

It is as easy as setting up POCO object match up with YAML file structure, you can read the whole file as enumerable pattern.

Listing 5.1 Read YAML File

var reader = new ChoYamlReader<EmployeeRec>("emp.yaml").WithYamlPath("$.emps[*]");
var rec = (object)null;
 
while ((rec = reader.Read()) != null)
{
    Console.WriteLine(e.Id);
    Console.WriteLine(e.Name);
}

6. Customize YAML Record

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

Listing 6.1 Customizing POCO Object for Each Record

[ChoYamlRecordObject]
public class EmployeeRec
{
    [ChoYamlRecordField] 
    public int Id { get; set; }
    [ChoYamlRecordField] 
    [Required]
    [DefaultValue("ZZZ")]
    public string Name { get; set; }
}

Here are the available attributes to carry out customization of YAML load operation on a file.

YamlPath - Optional. YamlPath expression used to pick the elements to load. If not specified, the member value will be discovered and loaded automatically.
CultureName - The culture name (e.g., en-US, en-GB) is used to read and write YAML data.
Encoding - The encoding of the YAML file.
ColumnCountStrict - This flag indicates if an exception should be thrown if reading an expected field is missing.
ErrorMode - This flag indicates if an exception should be thrown if reading and an expected field is failed to load. 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 IChoNotifyRecordRead type
- ThrowAndStop - Throw the error and stop the execution
IgnoreFieldValueMode - A flag to let the reader know if a record should be skipped when reading if it's empty / null. This can be overridden per property. Possible values are:
- Null - skipped if the record value is null
- DBNull - N/A
- Empty - skipped if the record value is empty
- WhiteSpace - skipped if the record value contains only whitespaces
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 (Default)
- MemberLevel - Validation performed at the time of each YAML property gets loaded with value
- ObjectLevel - Validation performed after all the properties are loaded to the POCO object

7. Customize YAML Fields

For each yaml field, you can specify the mapping in POCO entity property using ChoYamlRecordFieldAttribute. Only use this attribute if you want to use custom YamlPath to map to this field.

Listing 7.1 Customizing POCO Object for YAML Fields

public class EmployeeRec
{
    [ChoYamlRecordField]
    public int Id { get; set; }
    [ChoYamlRecordField]
    [Required]
    [DefaultValue("ZZZ")]
    public string Name { get; set; }
}

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

YamlPath - Optional. YamlPath expression uses a path notation for addressing parts of a YAML document. If not specified, ChoYamlReader automatically discovers and loads the value from YAML object matching field name.

7.1. DefaultValue

It is the value used and set to the property when the yaml value is empty or whitespace (controlled via IgnoreFieldValueMode).

Any POCO entity property can be specified with default value using System.ComponentModel.DefaultValueAttribute.

7.2. ChoFallbackValue

It is the value used and set to the property when the YAML value failed to set. Fallback value is only set when ErrorMode is either IgnoreAndContinue or ReportAndContinue.

Any POCO entity property can be specified with fallback value using ChoETL.ChoFallbackValueAttribute.

7.3. Type Converters

Most of the primitive types are automatically converted and set them to the properties. If the value of the yaml field can't automatically be converted into the type of the property, you can specify a custom / built-in .NET converters to convert the value. These can be either IValueConverter or TypeConverter converters.

There are a couple of ways in which you can specify the converters for each field:

Declarative Approach
Configuration Approach

7.3.1. Declarative Approach

This model is applicable to POCO entity object only. If you have POCO class, you can specify the converters to each property to carry out necessary conversion on them. Samples below show the way to do it.

Listing 7.3.1.1 Specifying Type Converters

public class EmployeeRec
{
    [ChoYamlRecordField]
    [ChoTypeConverter(typeof(IntConverter))]
    public int Id { get; set; }
    [ChoYamlRecordField]
    [Required]
    [DefaultValue("ZZZ")]
    public string Name { get; set; }
}

Listing 7.3.1.2 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)
    {
        return value;
    }
}

In the example above, we defined custom IntConverter class. And showed how to use it with 'Id' YAML property.

7.3.2. Configuration Approach

This model is applicable to both dynamic and POCO entity object. This gives freedom to attach the converters to each property at runtime. This takes precedence over the declarative converters on POCO classes.

Listing 7.3.2.2 Specifying TypeConverters

ChoYamlRecordConfiguration config = new ChoYamlRecordConfiguration();

ChoYamlRecordFieldConfiguration idConfig = new ChoYamlRecordFieldConfiguration("Id");
idConfig.AddConverter(new IntConverter());
config.YamlRecordFieldConfigurations.Add(idConfig);

config.YamlRecordFieldConfigurations.Add(new ChoYamlRecordFieldConfiguration("Name"));

In the above, we construct and attach the IntConverter to 'Id' field using AddConverter helper method in ChoYamlRecordFieldConfiguration object.

Likewise, if you want to remove any converter from it, you can use RemoveConverter on ChoYamlRecordFieldConfiguration object.

7.4. Validations

ChoYamlReader 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 7.4.1 Using Validation Attributes in POCO Entity

[ChoYamlRecordObject]
public partial class EmployeeRec
{
    [ChoYamlRecordField(FieldName = "id")]
    [ChoTypeConverter(typeof(IntConverter))]
    [Range(1, int.MaxValue, ErrorMessage = "Id must be > 0.")]
    [ChoFallbackValue(1)]
    public int Id { get; set; }
 
    [ChoYamlRecordField(FieldName = "Name")]
    [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. ChoYamlReader performs validation on them during load based on Configuration.ObjectValidationMode is set to ChoObjectValidationMode.MemberLevel or ChoObjectValidationMode.ObjectLevel.

Sometimes, you may want to override the defined declarative validation behaviors that come with POCO class, you can do with Cinchoo ETL via configuration approach. The sample below shows the way to override them.

static void ValidationOverridePOCOTest()
{
    ChoYamlRecordConfiguration config = new ChoYamlRecordConfiguration();
    var idConfig = new ChoYamlRecordFieldConfiguration("Id");
    idConfig.Validators = new ValidationAttribute[] { new RequiredAttribute() };
    config.YamlRecordFieldConfigurations.Add(idConfig);
    config.YamlRecordFieldConfigurations.Add
           (new ChoYamlRecordFieldConfiguration("Name"));
 
    using (var parser = new ChoYamlReader<EmployeeRec>("emp.yaml", config))
    {
        object rec;
        while ((rec = parser.Read()) != null)
        {
            Console.WriteLine(rec.ToStringEx());
        }
    }
}

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 7.4.2 Manual Validation on POCO Entity

[ChoYamlRecordObject]
public partial class EmployeeRec : IChoValidatable
{
    [ChoYamlRecordField(FieldName = "id")]
    [ChoTypeConverter(typeof(IntConverter))]
    [Range(1, int.MaxValue, ErrorMessage = "Id must be > 0.")]
    [ChoFallbackValue(1)]
    public int Id { get; set; }
 
    [ChoYamlRecordField(FieldName = "Name")]
    [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.

8. Callback Mechanism

ChoYamlReader offers industry standard YAML parsing out of the box to handle most of the parsing needs. If the parsing is not handling any of the needs, you can use the callback mechanism offered by ChoYamlReader to handle such situations. In order to participate in the callback mechanism, you can use either of the following models:

Using event handlers exposed by ChoYamlReader via IChoReader interface
Inheriting POCO entity object from IChoNotifyRecordRead / IChoNotifyFileRead / IChoNotifyRecordFieldRead interfaces
Inheriting DataAnnotation's MetadataType type object by IChoNotifyRecordRead / IChoNotifyFileRead / IChoNotifyRecordFieldRead interfaces
Inheriting IChoNotifyRecordFieldConfigurable / IChoNotifyRecordFieldConfigurable configuration interfaces

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

IChoReader exposes the below events:

BeginLoad - Invoked at the begin of the YAML file load
EndLoad - Invoked at the end of the YAML file load
BeforeRecordLoad - Raised before the YAML record load
AfterRecordLoad - Raised after YAML record load
RecordLoadError - Raised when YAML record load errors out
BeforeRecordFieldLoad - Raised before YAML field value load
AfterRecordFieldLoad - Raised after YAML field value load
RecordFieldLoadError - Raised when YAML field value errors out
SkipUntil - Raised before the YAML parsing kicks off to add custom logic to skip record lines.
DoWhile - Raised during YAML parsing where you can add custom logic to stop the parsing.

IChoNotifyRecordRead exposes the below methods:

BeforeRecordLoad - Raised before the YAML record load
AfterRecordLoad - Raised after YAML record load
RecordLoadError - Raised when YAML record load errors out

IChoNotifyFileRead exposes the below methods:

BeginLoad - Invoked at the begin of the YAML file load
EndLoad - Invoked at the end of the YAML file load
SkipUntil - Raised before the YAML parsing kicks off to add custom logic to skip record lines
DoWhile - Raised during YAML parsing where you can add custom logic to stop the parsing

IChoNotifyRecordFieldRead exposes the below methods:

BeforeRecordFieldLoad - Raised before yaml field value load
AfterRecordFieldLoad - Raised after yaml field value load
RecordFieldLoadError - Raised when yaml field value errors out

IChoNotifyRecordConfigurable exposes the below methods:

RecondConfigure - Raised for YAML record configuration

IChoNotifyRecordFieldConfigurable exposes the below methods:

RecondFieldConfigure - Raised for each yaml record field configuration

8.1. Using ChoYamlReader Events

This is a more direct and simplest way to subscribe to the callback events and handle your odd situations in parsing YAML files. The downside is that code can't be reusable as you do by implementing IChoNotifyRecordRead with POCO record object.

The sample below shows how to use the BeforeRecordLoad callback method to skip lines starting with '%' characters.

Listing 8.1.1 Using ChoYamlReader Callback Events

static void IgnoreLineTest()
{
    using (var parser = new ChoYamlReader("emp.yaml").WithYamlPath("$.emps[*]"))
    {
        parser.BeforeRecordLoad += (o, e) =>
        {
            if (e.Source != null)
            {
                e.Skip = !((IDictionary<string, object>)e.Source).ContainsKey("Name");
            }
        };
        foreach (var e in parser)
            Console.WriteLine(e.Dump());
    }
}

Likewise, you can use other callback methods as well with ChoYamlReader.

8.2. Implementing IChoNotifyRecordRead Interface

The sample below shows how to implement IChoNotifyRecordRead interface to direct POCO class.

Listing 8.2.1 Direct POCO Callback Mechanism Implementation

[ChoYamlRecordObject]
public partial class EmployeeRec : IChoNotifyRecordRead
{
    [ChoYamlRecordField(FieldName = "Id")]
    [ChoTypeConverter(typeof(IntConverter))]
    [Range(1, int.MaxValue, ErrorMessage = "Id must be > 0.")]
    [ChoFallbackValue(1)]
    public int Id { get; set; }
    
    [ChoYamlRecordField(FieldName = "Name")]
    [Required]
    [DefaultValue("ZZZ")]
    [ChoFallbackValue("XXX")]
    public string Name { get; set; }
 
    public bool AfterRecordLoad(object target, int index, object source)
    {
        throw new NotImplementedException();
    }
 
    public bool BeforeRecordLoad(object target, int index, ref object source)
    {
        throw new NotImplementedException();
    }
 
    public bool RecordLoadError(object target, int index, object source, Exception ex)
    {
        throw new NotImplementedException();
    }
}

The sample below shows how to attach Metadata class to POCO class by using MetadataTypeAttribute on it.

Listing 8.2 MetaDataType Based Callback Mechanism Implementation

[ChoYamlRecordObject]
public class EmployeeRecMeta : IChoNotifyRecordRead
{
    [ChoYamlRecordField(FieldName = "Id")]
    [ChoTypeConverter(typeof(IntConverter))]
    [Range(1, int.MaxValue, ErrorMessage = "Id must be > 0.")]
    [ChoFallbackValue(1)]
    public int Id { get; set; }

    [ChoYamlRecordField(FieldName = "Name")]
    [Required]
    [DefaultValue("ZZZ")]
    [ChoFallbackValue("XXX")]
    public string Name { get; set; }
 
    public bool AfterRecordLoad(object target, int index, object source)
    {
        throw new NotImplementedException();
    }
 
    public bool BeforeRecordLoad(object target, int index, ref object source)
    {
        throw new NotImplementedException();
    }
 
    public bool RecordLoadError(object target, int index, object source, Exception ex)
    {
        throw new NotImplementedException();
    }
} 

[MetadataType(typeof(EmployeeRecMeta))]
public partial class EmployeeRec
{
    public int Id { get; set; }
    public string Name { get; set; }
}

The sample below shows how to attach Metadata class for sealed or third party POCO class by using ChoMetadataRefTypeAttribute on it.

Listing 8.2.3 ChoMetaDataRefType Based Callback Mechanism Implementation

[ChoMetadataRefType(typeof(EmployeeRec))]
[ChoYamlRecordObject]
public class EmployeeRecMeta : IChoNotifyRecordRead
{
    [ChoYamlRecordField(FieldName = "id")]
    [ChoTypeConverter(typeof(IntConverter))]
    [Range(1, int.MaxValue, ErrorMessage = "Id must be > 0.")]
    [ChoFallbackValue(1)]
    public int Id { get; set; }

    [ChoYamlRecordField(FieldName = "Name")]
    [Required]
    [DefaultValue("ZZZ")]
    [ChoFallbackValue("XXX")]
    public string Name { get; set; }
 
    public bool AfterRecordLoad(object target, int index, object source)
    {
        throw new NotImplementedException();
    }
 
    public bool BeforeRecordLoad(object target, int index, ref object source)
    {
        throw new NotImplementedException();
    }
 
    public bool RecordLoadError(object target, int index, object source, Exception ex)
    {
        throw new NotImplementedException();
    }
} 

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

8.3. BeginLoad

This callback is invoked once at the beginning of the YAML file load. source is the YAML file stream object. In here, you have a chance to inspect the stream, return true to continue the YAML load. Returns false to stop the parsing.

Listing 8.1.1 BeginLoad Callback Sample

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

8.4. EndLoad

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

Listing 8.2.1 EndLoad Callback Sample

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

8.5. BeforeRecordLoad

This callback is invoked before each YAML node in the YAML file is loaded. target is the instance of the POCO record object. index is the JObject node index in the file. source is the YAML record object. In here, you have a chance to inspect the object, and override it with new values if want to.

TIP: If you want to skip the JObject from loading, set the source to null.