BuildNotContainsExpression

19 Apr 2009 1 mins Entity Framework, LINQ

Colin Meek wrote extremely handy method for using it as Contains method we know it’s on collections, but not supported in Entity Framework right now (v1/EF3.5). The method is called BuildContainsExpression. Today in MSDN forums I needed this, but negated. Thus I wrote the BuildNotContainsExpression. It’s just small change of original Colin’s method.

static Expression<Func<TElement, bool>> BuildNotContainsExpression<TElement, TValue>(Expression<Func<TElement, TValue>> valueSelector, IEnumerable<TValue> values)
{
    if (null == valueSelector) { throw new ArgumentNullException("valueSelector"); }
    if (null == values) { throw new ArgumentNullException("values"); }
    ParameterExpression p = valueSelector.Parameters.Single();
    // p => valueSelector(p) != values[0] && valueSelector(p) != ...
    if (!values.Any())
    {
        return e => true;
    }
    var equals = values.Select(value => (Expression)Expression.NotEqual(valueSelector.Body, Expression.Constant(value, typeof(TValue))));
    var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.And(accumulate, equal));
    return Expression.Lambda<Func<TElement, bool>>(body, p);
}

Jiří Činčura is .NET, C# and Firebird expert. He focuses on data and business layers, language constructs, parallelism, databases and performance. For almost two decades he contributes to open-source, i.e. FirebirdClient. He works as a senior software engineer for Microsoft. Frequent speaker and blogger at www.tabsoverspaces.com.