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using System; | |
using System.Linq; | |
using System.Linq.Expressions; | |
namespace Extensions | |
{ | |
public static class PredicateBuilder | |
{ | |
public enum CombinationLogic | |
{ | |
AND, | |
OR | |
} | |
public static Expression<Func<T, bool>> True<T>() { return f => true; } | |
public static Expression<Func<T, bool>> False<T>() { return f => false; } | |
public static Expression<Func<T, bool>> Or<T>( | |
this Expression<Func<T, bool>> expr1, | |
Expression<Func<T, bool>> expr2) | |
{ | |
var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>()); | |
return Expression.Lambda<Func<T, bool>> | |
(Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters); | |
} | |
public static Expression<Func<T, bool>> And<T>( | |
this Expression<Func<T, bool>> expr1, | |
Expression<Func<T, bool>> expr2) | |
{ | |
var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>()); | |
return Expression.Lambda<Func<T, bool>> | |
(Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters); | |
} | |
// S -> source type, Q -> query type | |
// Create Where Expression for source type using | |
// query type object which has same | |
// properties (by name and type*) | |
public static Expression<Func<S, bool>> BuildWhere<S, Q>( | |
Q query, | |
CombinationLogic combinationalLogic = CombinationLogic.AND) | |
{ | |
var predicate = (combinationalLogic == CombinationLogic.OR) ? | |
False<S>() : | |
True<S>(); | |
var queryProperties = typeof(Q).GetProperties(); | |
var sourceProperties = typeof(S).GetProperties(); | |
var expressionParameter = Expression.Parameter(typeof(S)); | |
foreach (var property in queryProperties) | |
{ | |
var propertyType = property.PropertyType; | |
var propertyValue = property.GetValue(query); | |
var sourceProperty = sourceProperties | |
.Where(p => p.Name == property.Name) | |
.FirstOrDefault(); | |
if (propertyValue is null || sourceProperty is null) | |
{ | |
continue; | |
} | |
//If the source has a value type prop and query | |
//waraps it as a nullable the unwarp the type | |
//and get the value | |
if (sourceProperty.PropertyType != propertyType && | |
propertyType.IsGenericType && | |
propertyType.GetGenericTypeDefinition() == typeof(Nullable<>)) | |
{ | |
propertyType = Nullable.GetUnderlyingType(propertyType); | |
propertyValue = Convert.ChangeType(propertyValue, propertyType); | |
} | |
//check to see if the source prop type equals | |
//query prop type | |
if (sourceProperty.PropertyType != propertyType) | |
{ | |
continue; | |
} | |
var expressionProperty = Expression.Property(expressionParameter, property.Name); | |
var expressionConstant = Expression.Constant(propertyValue, propertyType); | |
var expressionEqual = Expression.Equal(expressionProperty, expressionConstant); | |
var lambda = Expression.Lambda<Func<S, bool>>(expressionEqual, expressionParameter); | |
predicate = (combinationalLogic == CombinationLogic.OR) ? | |
Or(predicate, lambda) : | |
And(predicate, lambda); | |
} | |
return predicate; | |
} | |
} | |
} |
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