我在SQL中有一个过程,我试图转化为Linq:
SELECT O.Id, O.Name as Organization
FROM Organizations O
JOIN OrganizationsHierarchy OH ON O.Id=OH.OrganizationsId
where OH.Hierarchy like '%/12/%'
我最关心的一行是:
where OH.Hierarchy like '%/12/%'
我有一个存储层次结构的列,例如/1/3/12/,所以我只使用%/12/%来搜索它。
我的问题是,Linq或。net中使用百分号的等价是什么?
晚了,但是我把它放在一起,以便能够使用SQL Like样式通配符进行字符串比较:
public static class StringLikeExtensions
{
/// <summary>
/// Tests a string to be Like another string containing SQL Like style wildcards
/// </summary>
/// <param name="value">string to be searched</param>
/// <param name="searchString">the search string containing wildcards</param>
/// <returns>value.Like(searchString)</returns>
/// <example>value.Like("a")</example>
/// <example>value.Like("a%")</example>
/// <example>value.Like("%b")</example>
/// <example>value.Like("a%b")</example>
/// <example>value.Like("a%b%c")</example>
/// <remarks>base author -- Ruard van Elburg from StackOverflow, modifications by dvn</remarks>
/// <remarks>converted to a String extension by sja</remarks>
/// <seealso cref="https://stackoverflow.com/questions/1040380/wildcard-search-for-linq"/>
public static bool Like(this String value, string searchString)
{
bool result = false;
var likeParts = searchString.Split(new char[] { '%' });
for (int i = 0; i < likeParts.Length; i++)
{
if (likeParts[i] == String.Empty)
{
continue; // "a%"
}
if (i == 0)
{
if (likeParts.Length == 1) // "a"
{
result = value.Equals(likeParts[i], StringComparison.OrdinalIgnoreCase);
}
else // "a%" or "a%b"
{
result = value.StartsWith(likeParts[i], StringComparison.OrdinalIgnoreCase);
}
}
else if (i == likeParts.Length - 1) // "a%b" or "%b"
{
result &= value.EndsWith(likeParts[i], StringComparison.OrdinalIgnoreCase);
}
else // "a%b%c"
{
int current = value.IndexOf(likeParts[i], StringComparison.OrdinalIgnoreCase);
int previous = value.IndexOf(likeParts[i - 1], StringComparison.OrdinalIgnoreCase);
result &= previous < current;
}
}
return result;
}
/// <summary>
/// Tests a string containing SQL Like style wildcards to be ReverseLike another string
/// </summary>
/// <param name="value">search string containing wildcards</param>
/// <param name="compareString">string to be compared</param>
/// <returns>value.ReverseLike(compareString)</returns>
/// <example>value.ReverseLike("a")</example>
/// <example>value.ReverseLike("abc")</example>
/// <example>value.ReverseLike("ab")</example>
/// <example>value.ReverseLike("axb")</example>
/// <example>value.ReverseLike("axbyc")</example>
/// <remarks>reversed logic of Like String extension</remarks>
public static bool ReverseLike(this String value, string compareString)
{
bool result = false;
var likeParts = value.Split(new char[] {'%'});
for (int i = 0; i < likeParts.Length; i++)
{
if (likeParts[i] == String.Empty)
{
continue; // "a%"
}
if (i == 0)
{
if (likeParts.Length == 1) // "a"
{
result = compareString.Equals(likeParts[i], StringComparison.OrdinalIgnoreCase);
}
else // "a%" or "a%b"
{
result = compareString.StartsWith(likeParts[i], StringComparison.OrdinalIgnoreCase);
}
}
else if (i == likeParts.Length - 1) // "a%b" or "%b"
{
result &= compareString.EndsWith(likeParts[i], StringComparison.OrdinalIgnoreCase);
}
else // "a%b%c"
{
int current = compareString.IndexOf(likeParts[i], StringComparison.OrdinalIgnoreCase);
int previous = compareString.IndexOf(likeParts[i - 1], StringComparison.OrdinalIgnoreCase);
result &= previous < current;
}
}
return result;
}
}
如果您需要为单元测试这样的客户端操作提供LIKE功能,CodeProject的这个方法很好地模拟了通配符的行为。
有点像@史蒂夫·阿克曼的回答,但更全面。
/// Published on CodeProject: http://www.codeproject.com/Articles/
/// 608266/A-Csharp-LIKE-implementation-that-mimics-SQL-LIKE
/// </remarks>
public static bool Like(this string s, string match, bool CaseInsensitive = true)
{
//Nothing matches a null mask or null input string
if (match == null || s == null)
return false;
//Null strings are treated as empty and get checked against the mask.
//If checking is case-insensitive we convert to uppercase to facilitate this.
if (CaseInsensitive)
{
s = s.ToUpperInvariant();
match = match.ToUpperInvariant();
}
//Keeps track of our position in the primary string - s.
int j = 0;
//Used to keep track of multi-character wildcards.
bool matchanymulti = false;
//Used to keep track of multiple possibility character masks.
string multicharmask = null;
bool inversemulticharmask = false;
for (int i = 0; i < match.Length; i++)
{
//If this is the last character of the mask and its a % or * we are done
if (i == match.Length - 1 && (match[i] == '%' || match[i] == '*'))
return true;
//A direct character match allows us to proceed.
var charcheck = true;
//Backslash acts as an escape character. If we encounter it, proceed
//to the next character.
if (match[i] == '\\')
{
i++;
if (i == match.Length)
i--;
}
else
{
//If this is a wildcard mask we flag it and proceed with the next character
//in the mask.
if (match[i] == '%' || match[i] == '*')
{
matchanymulti = true;
continue;
}
//If this is a single character wildcard advance one character.
if (match[i] == '_')
{
//If there is no character to advance we did not find a match.
if (j == s.Length)
return false;
j++;
continue;
}
if (match[i] == '[')
{
var endbracketidx = match.IndexOf(']', i);
//Get the characters to check for.
multicharmask = match.Substring(i + 1, endbracketidx - i - 1);
//Check for inversed masks
inversemulticharmask = multicharmask.StartsWith("^");
//Remove the inversed mask character
if (inversemulticharmask)
multicharmask = multicharmask.Remove(0, 1);
//Unescape \^ to ^
multicharmask = multicharmask.Replace("\\^", "^");
//Prevent direct character checking of the next mask character
//and advance to the next mask character.
charcheck = false;
i = endbracketidx;
//Detect and expand character ranges
if (multicharmask.Length == 3 && multicharmask[1] == '-')
{
var newmask = "";
var first = multicharmask[0];
var last = multicharmask[2];
if (last < first)
{
first = last;
last = multicharmask[0];
}
var c = first;
while (c <= last)
{
newmask += c;
c++;
}
multicharmask = newmask;
}
//If the mask is invalid we cannot find a mask for it.
if (endbracketidx == -1)
return false;
}
}
//Keep track of match finding for this character of the mask.
var matched = false;
while (j < s.Length)
{
//This character matches, move on.
if (charcheck && s[j] == match[i])
{
j++;
matched = true;
break;
}
//If we need to check for multiple charaters to do.
if (multicharmask != null)
{
var ismatch = multicharmask.Contains(s[j]);
//If this was an inverted mask and we match fail the check for this string.
//If this was not an inverted mask check and we did not match fail for this string.
if (inversemulticharmask && ismatch ||
!inversemulticharmask && !ismatch)
{
//If we have a wildcard preceding us we ignore this failure
//and continue checking.
if (matchanymulti)
{
j++;
continue;
}
return false;
}
j++;
matched = true;
//Consumse our mask.
multicharmask = null;
break;
}
//We are in an multiple any-character mask, proceed to the next character.
if (matchanymulti)
{
j++;
continue;
}
break;
}
//We've found a match - proceed.
if (matched)
{
matchanymulti = false;
continue;
}
//If no match our mask fails
return false;
}
//Some characters are left - our mask check fails.
if (j < s.Length)
return false;
//We've processed everything - this is a match.
return true;
}