学习并使用了两种linq to entity 的实现sql关键字in的查询方法

//构造Lambda语句
private static Expression<Func<TElement, bool>> BuildWhereInExpression<TElement, TValue>(Expression<Func<TElement, TValue>> propertySelector, IEnumerable<TValue> values)
{
ParameterExpression p = propertySelector.Parameters.Single();
if (!values.Any())
return e => false;

var equals = values.Select(value => (Expression)Expression.Equal(propertySelector.Body, Expression.Constant(value, typeof(TValue))));
var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.Or(accumulate, equal));

return Expression.Lambda<Func<TElement, bool>>(body, p);
}

//调用
string[] ids = new string[]{"id1","id2","id3"}；
db.ProjectFiles.Where(BuildWhereInExpression<Profile,int>(v=>v.Id,ids);

//封装方法

public static IQueryable<TElement> WhereIn<TElement, TValue>(this IQueryable<TElement> source, Expression<Func<TElement, TValue>> propertySelector, params TValue[] values)
{
return source.Where(BuildWhereInExpression(propertySelector, values));
}
//直接使用下列方法调用

string[] ids = new string[]{"id1","id2","id3"}；
db.ProjectFiles.WhereIn(c => c.Id,ids);
//字符串构造
//这个方法比较简单

string[] ids = new string[]{"id1","id2","id3"}；
cstIds=cstIds.Replace(",","','");
var query = db.ProjectFiles.Where("it.Id in {'" + cstIds + "'}");