我想使用Dapper扩展谓词替换此查询吗?
SELECT *
FROM SomeTable
WHERE id IN (commaSeparatedListOfIDs)
commaSeparatedListOfIDs
是IEnumerable
的Integer
。到目前为止我尝试过的是:
using (SqlConnection cn = new SqlConnection(_connectionString))
{
cn.Open();
var predicate = Predicates.Field<SomeTable>(f => f.Id, Operator.???, commaSeparatedListOfIDs);
IEnumerable<SomeTable> list = cn.GetList<SomeTable>(predicate);
cn.Close();
}
我需要一个运算符
Operator.In
,但Dapper Extensions中不存在该运算符。如何在Dapper Extensions谓词系统中实现“ IN”子句?
最佳答案
解决方案1:
将PredicateGroup
与GroupOperator.Or
一起使用是一种解决方案。
var predicateGroup = new PredicateGroup { Operator = GroupOperator.Or, Predicates = new List<IPredicate>() };
foreach(int thisID in commaSeparatedListOfIDs)
{
var predicate = Predicates.Field<SomeTable>(f => f.Id, Operator.Eq, thisID);
predicateGroup.Predicates.Add(predicate);
}
IEnumerable<SomeTable> list = cn.GetList<SomeTable>(predicateGroup);
请参考this链接。
解决方案2:
正如您在答案和this链接中提到的那样,将FieldPredicate(
Predicates.Field
)与Operator.Eq
一起使用,并传递IEnumerable
参数应该可以做到这一点。var predicate = Predicates.Field<SomeTable>(f => f.Id, Operator.Eq, commaSeparatedListOfIDs);
根据GitHub上Dapper Extensions的this源代码,此处
Eq
应该在内部转换为IN子句。if(Value is IEnumerable && !(Value is string))
{
if(Operator != Operator.Eq)
{
throw new ArgumentException("Operator must be set to Eq for Enumerable types");
}
List<string> @params = new List<string>();
foreach(var value in (IEnumerable)Value)
{
string valueParameterName = parameters.SetParameterName(this.PropertyName, value, sqlGenerator.Configuration.Dialect.ParameterPrefix);
@params.Add(valueParameterName);
}
string paramStrings = @params.Aggregate(new StringBuilder(), (sb, s) => sb.Append((sb.Length != 0 ? ", " : string.Empty) + s), sb => sb.ToString());
return string.Format("({0} {1}IN ({2}))", columnName, Not ? "NOT " : string.Empty, paramStrings);
}
关于c# - 如何使用Dapper Extensions谓词实现“IN”子句?,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/49777139/