Lambda/Linq with Contains criteria for multiple keywords

Question

I have to lists

1. Main list with Comments field
2. List of keywords to search for.

I want to search the keywords in each Comment field of each record which in SQL would look like below

select * from MainList
where Comment like '%keyword1%'
or Comment like '%keyword2%'
... so on until the last keyword.

So far I have seen examples but usually for single keyword at a time only e.g. LINQ with non-lambda for Any Contains

What I would like is to search each record in MainList for any instance of any of my keyowrds all at once. something like:

var newList = MainList.Where(m => m.Comments.Contains(purposes))

I would prefer doing it in lambda syntax but if not possible, linq is also okay.

Answer 1

Added extension method which can help in generating such predicate. Usage is simple:

var newList = MainList
   .FilterByItems(keywords, (m, k) => m.Comments.Contains(k), true)
   .ToList();

And implementation:

public static class QueryableExtensions
{
    public static IQueryable<T> FilterByItems<T, TItem>(this IQueryable<T> query, IEnumerable<TItem> items,
        Expression<Func<T, TItem, bool>> filterPattern, bool isOr)
    {
        Expression predicate = null;
        foreach (var item in items)
        {
            var itemExpr = Expression.Constant(item);
            var itemCondition = ExpressionReplacer.Replace(filterPattern.Body, filterPattern.Parameters[1], itemExpr);
            if (predicate == null)
                predicate = itemCondition;
            else
            {
                predicate = Expression.MakeBinary(isOr ? ExpressionType.OrElse : ExpressionType.AndAlso, predicate,
                    itemCondition);
            }
        }

        predicate ??= Expression.Constant(false);
        var filterLambda = Expression.Lambda<Func<T, bool>>(predicate, filterPattern.Parameters[0]);

        return query.Where(filterLambda);
    }

    class ExpressionReplacer : ExpressionVisitor
    {
        readonly IDictionary<Expression, Expression> _replaceMap;

        public ExpressionReplacer(IDictionary<Expression, Expression> replaceMap)
        {
            _replaceMap = replaceMap ?? throw new ArgumentNullException(nameof(replaceMap));
        }

        public override Expression Visit(Expression exp)
        {
            if (exp != null && _replaceMap.TryGetValue(exp, out var replacement))
                return replacement;
            return base.Visit(exp);
        }

        public static Expression Replace(Expression expr, Expression toReplace, Expression toExpr)
        {
            return new ExpressionReplacer(new Dictionary<Expression, Expression> { { toReplace, toExpr } }).Visit(expr);
        }

        public static Expression Replace(Expression expr, IDictionary<Expression, Expression> replaceMap)
        {
            return new ExpressionReplacer(replaceMap).Visit(expr);
        }

        public static Expression GetBody(LambdaExpression lambda, params Expression[] toReplace)
        {
            if (lambda.Parameters.Count != toReplace.Length)
                throw new InvalidOperationException();

            return new ExpressionReplacer(Enumerable.Range(0, lambda.Parameters.Count)
                .ToDictionary(i => (Expression) lambda.Parameters[i], i => toReplace[i])).Visit(lambda.Body);
        }
    }
}

Answer 2

Answering for my and others' reference.

var newList = MainList.Where(m => keywords.Any(k => m.Comments.Contains(k))).ToList();