Suppose I have a table, containing formatted values in a string ( nvarchar
) column. These values are supposed to be strings separated by some const symbol (let it be a semi-colon ;
). For example,
12;0;5;dog //four values separated by a semi-colon
or
053 //if there is only one value, no semi-colon at the end
The separator is always a separator, it can't be a part of the value.
I need to check if there is already a row in that table, with a list of values in that column, which contains at least one of the specified items. In other words I have a list of values:
List<string> list = new List<string>() { "somevalue1", "somevalue2" };
the separator:
string separator = ";";
And I need to write a linq-to-sql query doing this:
select ... from sometable
where Value='somevalue1' or Value like 'somevalue1;%' or
Value like '%;somevalue1' or Value like '%;somevalue1;%'
or Value='somevalue2' or Value like 'somevalue2;%' or
Value like '%;somevalue2' or Value like '%;somevalue2;%'
It should be mentioned that any of the searched values may contain the other. That is, I may be searching for exactly 5
, while some row may contain 1;15;55
. Such row must not be a match. While ...;5;...
or just 5
, or 5;...
, or ...;5
are the matches.
Using linq-to sql I know how to do queries of the following kind:
select ... from sometable where (... or ... or ...) and (... or ...) ...
that is
IQueryable<SomeTable> query = dc.SomeTable;
foreach (string l in list)
{
string s = l;
query = query.Where(b => b.Value.StartsWith(s + separator) ||
b.Value.EndsWith(separator + s) ||
b.Value.Contains(separator + s + separator) ||
b.Value.Equals(s));
}
if (query.Any()) {/*...*/}
Obviously the Where
statements are joined with AND
in the resulting sql query, while I need OR
everywhere.
So is there a way to get the query I need within C# code? Or the only way would be to do this with a hand-written query and DataContext.ExecuteQuery Method ?
I guess a UNION
would suit your needs:
IQueryable<SomeTable> baseQuery = dc.SomeTable;
IQueryable<SomeTable> query = new List<SomeTable>().AsQueryable();
foreach (string l in list)
{
string s = l;
query.Union(baseQuery.Where(b => b.Value.StartsWith(s + separator) ||
b.Value.EndsWith(separator + s) ||
b.Value.Contains(separator + s + separator) ||
b.Value.Equals(s)));
}
if (query.Any()) {/*...*/}
public static Expression<Func<T, bool>> OrTheseFiltersTogether<T>(
this IEnumerable<Expression<Func<T, bool>>> filters)
{
Expression<Func<T, bool>> firstFilter = filters.FirstOrDefault();
if (firstFilter == null)
{
Expression<Func<T, bool>> alwaysTrue = x => true;
return alwaysTrue;
}
var body = firstFilter.Body;
var param = firstFilter.Parameters.ToArray();
foreach (var nextFilter in filters.Skip(1))
{
var nextBody = Expression.Invoke(nextFilter, param);
body = Expression.OrElse(body, nextBody);
}
Expression<Func<T, bool>> result = Expression.Lambda<Func<T, bool>>(body, param);
return result;
}
So, you can build a List of filters easily from the input set:
List<string> list = new List<string>() { "somevalue1", "somevalue2" };
List<Expression<Func<SomeTable, bool>>> equalsFilters = list
.Select(s => row => row.Value == s).ToList();
List<Expression<Func<SomeTable, bool>>> startsWithFilters = list
.Select(s => row => row.Value.StartsWith(s + ";")).ToList();
List<Expression<Func<SomeTable, bool>>> endsWithFilters = list
.Select(s => row => row.Value.EndsWith(";" + s).ToList();
List<Expression<Func<SomeTable, bool>>> middleFilters = list
.Select(s => row => row.Value.Contains(";" + s + ";")).ToList();
Expression<Func<SomeTable, bool>> theFilter = OrTheseFiltersTogether(
equalsFilters.Concat(startsWithFilters).Concat(endsWithFilters).Concat(middleFilters)
);
query = query.Where(theFilter);
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