HLCores.Utilities.PredicateBuilder 4.0.0

HLCores.Utilities.PredicateBuilder

HLCores.Utilities.PredicateBuilder is a design pattern (often implemented as a utility class) that allows you to dynamically build LINQ expression trees at runtime — especially for Where() clauses with optional or conditional filters .

🎯 Purpose

To dynamically generate filtering conditions for LINQ depending on the type and value of param:

• If param is a string → performs keyword search across common text fields.
• If param is a single value → compares it with a property (default is "Id").
• If param is a class object → builds combined conditions based on each property value, optionally enhanced with attributes.

✅ 1. param is a string (e.g. search keyword)To dynamically generate a .Where(...) filter like:

BuildPredicate<Product, string>("abc")

• Filters by fields like: Code, Title, Description, Email, etc.
• Uses .ToLower().Contains(keyword) to match values case-insensitively.

✅ 2. param is a single value (e.g. int, Guid)

BuildPredicate<User, Guid>(userId)

• Creates simple comparison: x => x.Id == userId (or a different property if paramName is specified).

✅ 3. param is an object with multiple properties

BuildPredicate<Product, ProductFilter>(filter)

• Each non-null property in filter is matched with the corresponding property in TModel.
• Optional support for PredicateFilterAttribute allows you to define:
  • Comparison operator (=, LIKE, >, <, IN, etc.)
  • Logical operator (AND, OR)
  • Grouping of conditions using group (for compound filters)

🔧 Example of PredicateFilterAttribute

public class ProductFilter
{
    [PredicateFilter(CompareOperator = SqlCompareOperatorConstants.LIKE)]
    public string? Name { get; set; }

    [PredicateFilter(CompareOperator = SqlCompareOperatorConstants.GREATER_THAN_OR_EQUAL_TO)]
    public decimal? MinPrice { get; set; }

    [PredicateFilter(CompareOperator = SqlCompareOperatorConstants.LESS_THAN_OR_EQUAL_TO)]
    public decimal? MaxPrice { get; set; }
}

x => x.Name.Contains("...") && x.Price >= ... && x.Price <= ...

📦 Return value

• If no valid conditions found → returns x => true (no filtering).
• Otherwise → returns a composed predicate for .Where(...).

📘 Usage example

Expression<Func<Product, bool>> predicate = PredicateBuilderUtility.BuildPredicate<Product, ProductFilter>(filter);
var result = dbContext.Products.Where(predicate);