Does Dapper support the like operator?

问题:

Using Dapper-dot-net...

The following yields no results in the data object:

var data = conn.Query(@"
    select top 25 
    Term as Label, 
    Type, 
    ID 
    from SearchTerms 
    WHERE Term like '%@T%'", 
    new { T = (string)term });

However, when I just use a regular String Format like:

string QueryString = String.Format("select top 25 Term as Label, Type, ID from SearchTerms WHERE Term like '%{0}%'", term);
var data = conn.Query(QueryString);

I get 25 rows back in the collection. Is Dapper not correctly parsing the end of the parameter @T?

回答1:

Try:

term = "whateverterm";
var encodeForLike = term => term.Replace("[", "[[]").Replace("%", "[%]");

string term = "%" + encodeForLike(term) + "%";
var data = conn.Query(@"
   select top 25 
  Term as Label, 
  Type, 
  ID 
  from SearchTerms 
  WHERE Term like @term", 
  new { term });

There is nothing special about like operators, you never want your params inside string literals, they will not work, instead they will be interpreted as a string.

note

The hard-coded example in your second snippet is strongly discouraged, besides being a huge problem with sql injection, it can cause dapper to leak.

caveat

Any like match that is leading with a wildcard is not SARGable, which means it is slow and will require an index scan.

回答2:

Best way to use this to add concat function in query as it save in sql injecting as well, but concat function is only support above than sql 2012

string query = "SELECT * from country WHERE Name LIKE CONCAT('%',@name,'%');"
var results = connection.query<country>(query, new {name});

回答3:

Yes it does. This simple solution has worked for me everytime:

db.Query<Remitente>("SELECT * 
                     FROM Remitentes 
                     WHERE Nombre LIKE @n", new { n = "%" + nombre + "%" })
                   .ToList();

回答4:

The answer from Sam wasn't working for me so after some testing I came up with using the SQLite CONCAT equivalent which seems to work:

string sql = "SELECT * FROM myTable WHERE Name LIKE '%' || @NAME || '%'";
var data = IEnumerable data = conn.Query(sql, new { NAME = Name });