LINQ Contains Case Insensitive

Question

This code is case sensitive  how to make it case insensitive    public IQueryable lt FACILITY ITEM gt  GetFacilityItemRootByDescription string description        return this ObjectContext FACILITY ITEM Where fi   gt  fi DESCRIPTION Contains description

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public static bool Contains this string input  string findMe  StringComparison comparisonType        return String IsNullOrWhiteSpace input    false   input IndexOf findMe  comparisonType   gt  -1

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Assuming we re working with strings here  here s another  elegant  solution using IndexOf     public IQueryable lt FACILITY ITEM gt  GetFacilityItemRootByDescription string description        return this ObjectContext FACILITY ITEM          Where fi   gt  fi DESCRIPTION                         IndexOf description  StringComparison OrdinalIgnoreCase     -1

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Use String Equals Method  public IQueryable lt FACILITY ITEM gt  GetFacilityItemRootByDescription string description        return this ObjectContext FACILITY ITEM             Where fi   gt  fi DESCRIPTION             Equals description  StringComparison OrdinalIgnoreCase

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Using C  6 0  which allows expression bodied functions and null propagation   for LINQ to Objects  it can be done in a single line like this  also checking for null    public static bool ContainsInsensitive this string str  string value    gt  str  IndexOf value  StringComparison OrdinalIgnoreCase   gt   0

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If the LINQ query is executed in database context  a call to Contains   is mapped to the LIKE operator    Where a   gt  a Field Contains  hello     becomes Field LIKE   hello    The LIKE operator is case insensitive by default  but that can be changed by changing the collation of the column   If the LINQ query is executed in  NET context  you can use IndexOf    but that method is not supported in LINQ to SQL   LINQ to SQL does not support methods that take a CultureInfo as parameter  probably because it can not guarantee that the SQL server handles cultures the same as  NET  This is not completely true  because it does support StartsWith string  StringComparison    However  it does not seem to support a method which evaluates to LIKE in LINQ to SQL  and to a case insensitive comparison in  NET  making it impossible to do case insensitive Contains   in a consistent way

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IndexOf works best in this case  return this     ObjectContext     FACILITY ITEM     Where fi   gt  fi DESCRIPTION IndexOf description  StringComparison OrdinalIgnoreCase  gt  0

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You can use string Compare      lst Where x   gt  string Compare x  valueToCompare  StringComparison InvariantCultureIgnoreCase   0     if you just want to check contains then use  Any     lst Any x   gt  string Compare x  valueToCompare  StringComparison InvariantCultureIgnoreCase   0

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StringComparison InvariantCultureIgnoreCase just do the job for me     Where fi   gt  fi DESCRIPTION Contains description  StringComparison InvariantCultureIgnoreCase

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fi   gt  fi DESCRIPTION ToLower   Contains description ToLower

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The accepted answer here does not mention a fact that if you have a null string ToLower   will throw an exception  The safer way would be to do   fi   gt   fi DESCRIPTION    string Empty  ToLower   Contains  description    string Empty  ToLower

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Honestly  this doesn t need to be difficult  It may seem that on the onset  but it s not  Here s a simple linq query in C  that does exactly as requested   In my example  I m working against a list of persons that have one property called FirstName    var results   ClientsRepository   Where c   gt  c FirstName ToLower   Contains searchText ToLower     ToList      This will search the database on lower case search but return full case results

[c#] LINQ Contains Case Insensitive

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