原始SQL的运行速度是否快于等效的LINQ方法？

Question

I have this method that returns the Count of rows with the given search criteria:

public int HistoryCount(Guid id, string tableName)
{
    int sqlCount = context.Database.SqlQuery<int>("SELECT COUNT(*) FROM 
        COMMON.TbHistoryLog WHERE ObjectId = '" + id + "' 
        AND TableName = '" + tableName + "'").First();
    FuncHistory = x => x.ObjectId == id && x.TableName == tableName;
    return AuditHelper.HistoryCount(context.TbHistoryLog, FuncHistory);
}

and this is AuditHelper.HistoryCount method:

public static int HistoryCount<TSet>(DbSet<TSet> set, Func<TSet, bool> predict) where TSet : class
{
    var auditCount = set.Count(predict);
    return auditCount;
}

I was running into long querying time when executing AuditHelper.HistoryCount method, and then I tried to run the same query (I guess) using raw SQL, which returned the result immediately.

Is there something wrong with my implementation or raw SQL is faster than the equivalent LINQ methods?

Answer 1

Because you are using Count(Func<>) in your helper function, you are calling Enumerable.Count() which means you are pulling all records from the database and then processing the predicate and count locally. You need to use Expression<Func<>> to use Queryable.Count() that will be processed by the SQL server:

public static int HistoryCount<TSet>(DbSet<TSet> set, Expression<Func<TSet, bool>> predict) where TSet : class {
    var auditCount = set.Count(predict);
    return auditCount;
}

Then code it like so:

return AuditHelper.HistoryCount(context.TbHistoryLog, x => x.ObjectId == id && x.TableName == tableName);

Or declare FuncHistory to be Expression :

Expression<Func<TBHistoryLog, bool>> FuncHistory = x => x.ObjectId == id && x.TableName == tableName;