LINQ如何包含工作 [英] How does LINQ contains work

问题描述

我了解如何使用LINQ，因此语法在这里并不重要. LINQ如何精确地穿透包含"，并且背景中发生了什么?我了解它会找到包含您要查找的单词的所有元素，但是会找到包含多个未包含的单词的结果吗?例如，我在数据库中有一个用于输入名称的行，如果使用包含，我就能找到

I understand how to use LINQ so the syntax is not important here. How exactly does LINQ interpenetrate "contains" and what is going on in the background? I understand that it finds all the elements that have the word you are looking for but will it find a result with multiple words that are not all contained? For example I have a row in a database for a name and if i use contains will I be able to find my person with

Contains("James Bar") 

如果真名是James foo Bar

If the real name is James foo Bar

还是查询只是寻找

where name like '%James bar%'

不返回结果

推荐答案

在这里，我们去---通过

Here we go --- check it out via reference source: Contains calls IndexOf with a greater equal comparison and that calls an overloaded IndexOf method. hth

        [Pure]
        public bool Contains( string value ) {
             return ( IndexOf(value, StringComparison.Ordinal) >=0 );
        }

        [Pure]
        public int IndexOf(String value, StringComparison comparisonType) {
            return IndexOf(value, 0, this.Length, comparisonType);
        }

        [Pure]
        [System.Security.SecuritySafeCritical]
        public int IndexOf(String value, int startIndex, int count, StringComparison comparisonType) {
            // Validate inputs
            if (value == null)
                throw new ArgumentNullException("value");

            if (startIndex < 0 || startIndex > this.Length)
                throw new ArgumentOutOfRangeException("startIndex", Environment.GetResourceString("ArgumentOutOfRange_Index"));

            if (count < 0 || startIndex > this.Length - count)
                throw new ArgumentOutOfRangeException("count", Environment.GetResourceString("ArgumentOutOfRange_Count"));
            Contract.EndContractBlock();

            switch (comparisonType) {
                case StringComparison.CurrentCulture:
                    return CultureInfo.CurrentCulture.CompareInfo.IndexOf(this, value, startIndex, count, CompareOptions.None);

                case StringComparison.CurrentCultureIgnoreCase:
                    return CultureInfo.CurrentCulture.CompareInfo.IndexOf(this, value, startIndex, count, CompareOptions.IgnoreCase);

                case StringComparison.InvariantCulture:
                    return CultureInfo.InvariantCulture.CompareInfo.IndexOf(this, value, startIndex, count, CompareOptions.None);

                case StringComparison.InvariantCultureIgnoreCase:
                    return CultureInfo.InvariantCulture.CompareInfo.IndexOf(this, value, startIndex, count, CompareOptions.IgnoreCase);

                case StringComparison.Ordinal:
                    return CultureInfo.InvariantCulture.CompareInfo.IndexOf(this, value, startIndex, count, CompareOptions.Ordinal);

                case StringComparison.OrdinalIgnoreCase:
                    if (value.IsAscii() && this.IsAscii())
                        return CultureInfo.InvariantCulture.CompareInfo.IndexOf(this, value, startIndex, count, CompareOptions.IgnoreCase);
                    else
                        return TextInfo.IndexOfStringOrdinalIgnoreCase(this, value, startIndex, count);

                default:
                    throw new ArgumentException(Environment.GetResourceString("NotSupported_StringComparison"), "comparisonType");
            }  
        }

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