public static Expression <Func <T, bool> > BuildOperation <T>(Func <Expression, Expression, Expression> bodyFunc, string propertyName, object value)
{
ParameterExpression param = Expression.Parameter(typeof(T), propertyName);
LambdaExpression lambda = DynamicExpression.ParseLambda(typeof(T), null, propertyName, null);
var leftVisitor = new ReplaceExpressionVisitor(lambda.Parameters[0], param);
var left = leftVisitor.Visit(lambda.Body);
ConstantExpression constant = Expression.Constant(value, lambda.Body.Type);
var body = bodyFunc(left, constant);
return(Expression.Lambda <Func <T, bool> >(body, param));
}
public static Expression <Func <T, bool> > AndAlso <T>(
this Expression <Func <T, bool> > expr1,
Expression <Func <T, bool> > expr2)
{
if (expr1 == null)
{
return(expr2);
}
if (expr2 == null)
{
return(expr1);
}
var parameter = Expression.Parameter(typeof(T));
var leftVisitor = new ReplaceExpressionVisitor(expr1.Parameters[0], parameter);
var left = leftVisitor.Visit(expr1.Body);
var rightVisitor = new ReplaceExpressionVisitor(expr2.Parameters[0], parameter);
var right = rightVisitor.Visit(expr2.Body);
return(Expression.Lambda <Func <T, bool> >(
Expression.AndAlso(left, right), parameter));
}