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log : Debug Logging Helper

Output debug messages to the trace log during template processing. Useful for debugging data binding and template logic. Does not render any visible content in the PDF.

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Syntax

{{log message}}
{{log message1 expression message2 level="info" category="debug"}}

Parameters

Parameter Type Required Description
message(s) String/Expression Yes One or more strings or expressions to log (concatenated)
level String No Log level: debug, info, warn, error (default: info)
category String No Category for filtering log messages (optional)

Log Levels

Level Description Use Case
debug Verbose debugging Detailed tracing during development
info Informational General information (default)
warn Warning Potential issues that don’t stop execution
error Error Significant problems worth noting

Examples

Basic Logging

{{log "Processing user profile"}}

Logging Values

{{#with model.user}}
  {{log "User: " name " (ID: " id ")"}}
{{/with}}

Data:

doc.Params["model"] = new {
    user = new {
        name = "John Doe",
        id = 12345
    }
};

Log Output:

User: John Doe (ID: 12345)

With Log Level

{{log "Starting data processing" level="debug"}}

{{#if model.hasError}}
  {{log "Error processing order: " model.errorMessage level="error"}}
{{/if}}

{{log "Processing complete" level="info"}}

With Category for Filtering

{{log "Validating user input" category="validation"}}

{{#if model.isValid}}
  {{log "Validation passed" category="validation" level="info"}}
{{else}}
  {{log "Validation failed: " model.validationErrors category="validation" level="warn"}}
{{/if}}

Logging in Loops

{{#each model.orders}}
  {{log "Processing order #" this.orderNumber category="orders"}}

  {{#if this.total > 1000}}
    {{log "High-value order: $" this.total level="info" category="orders"}}
  {{/if}}
{{/each}}

Data:

doc.Params["model"] = new {
    orders = new[] {
        new { orderNumber = "12345", total = 1250.00m },
        new { orderNumber = "12346", total = 45.99m },
        new { orderNumber = "12347", total = 2100.00m }
    }
};

Log Output:

Processing order #12345
High-value order: $1250
Processing order #12346
Processing order #12347
High-value order: $2100

Logging with Expressions

{{#with model.user}}
  {{log if(isModerator, "User is a moderator", "User is not a moderator") level="debug" category="auth"}}

  {{log "User " name " has " concat(format(loginCount, 'N0'), " logins") category="stats"}}
{{/with}}

Conditional Debugging

{{#each model.items}}
  {{#if this.price > 100}}
    {{log "Expensive item: " this.name " ($" this.price ")" level="warn" category="pricing"}}
  {{/if}}

  {{#if this.stock <= 0}}
    {{log "Out of stock: " this.name level="error" category="inventory"}}
  {{/if}}
{{/each}}

Underlying Implementation

The {{log}} helper compiles to:

<log data-message="{{concatenated expressions}}"
     data-level="Verbose|Message|Warning|Error"
     data-category="category name" />

The log entry is written to the document’s trace log during databinding and does not produce any visible output in the PDF.

Notes

  • Does not render any visible content in the PDF
  • Messages are written to the document’s trace log
  • Multiple values are automatically concatenated with spaces
  • Supports expressions (function calls, property access, etc.)
  • Unknown parameters are silently ignored
  • Use doc.AppendTraceLog = true to enable logging in C#
  • View log output in CollectorTraceLog for unit testing
  • Category helps filter log messages for specific features
  • Log level affects visibility based on trace log configuration
  • Useful for debugging complex conditional logic and iterations

Enabling Trace Logging

To see log output, enable trace logging in your document:

doc.AppendTraceLog = true;
doc.SaveAsPDF(output);

// Access log entries
var collector = doc.TraceLog as CollectorTraceLog;
foreach (var entry in collector)
{
    Console.WriteLine($"[{entry.Level}] {entry.Category}: {entry.Message}");
}

See Also