Skip Policies

Skip policies let your job tolerate errors in individual records without aborting the entire step. When a skippable exception occurs, NBatch logs it, increments the skip counter, and moves on to the next item.

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Basic Usage

.AddStep("import", step => step
    .ReadFrom(reader)
    .WriteTo(writer)
    .WithSkipPolicy(SkipPolicy.For<FlatFileParseException>(maxSkips: 5)))

This tells the step: “If a FlatFileParseException is thrown, skip that record. If more than 5 records fail, abort the step.”

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Creating Skip Policies

Single Exception Type

SkipPolicy.For<FlatFileParseException>(maxSkips: 10)

Multiple Exception Types

SkipPolicy.For<FlatFileParseException, FormatException>(maxSkips: 5)

// Up to three types
SkipPolicy.For<FlatFileParseException, FormatException, InvalidOperationException>(maxSkips: 5)

No Skipping (Default)

If you don’t specify a skip policy, the step uses SkipPolicy.None – any exception aborts the step immediately.

SkipPolicy.None  // default -- no tolerance for errors

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How It Works

1. During chunk processing, if an exception is thrown during read or process…
2. NBatch checks if the exception type matches the skip policy.
3. If it matches and the skip count is below the limit — the item is skipped.
4. If it doesn’t match, or the limit is exceeded — the exception propagates and the step fails.
5. Skipped errors are persisted in the job store (when enabled) for auditing.

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Monitoring Skips

The StepResult reports how many items were skipped:

var result = await job.RunAsync();

foreach (var step in result.Steps)
{
    Console.WriteLine($"Step: {step.Name}");
    Console.WriteLine($"  Read:    {step.ItemsRead}");
    Console.WriteLine($"  Written: {step.ItemsProcessed}");
    Console.WriteLine($"  Skipped: {step.ErrorsSkipped}");
}

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Best Practices

• Be specific about exception types – avoid SkipPolicy.For<Exception>(...) which swallows everything.
• Set reasonable limits – a high skip count may mask a systemic problem in your data.
• Use listeners to alert when skips occur – combine with IStepListener for monitoring.
• Enable the job store to persist skip details for post-mortem analysis.

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Next: Job Store →