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by Jiří {x2} Činčura


19 Apr 2009 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);