[英]Entity Framework: Count() very slow on large DbSet and complex WHERE clause
我需要使用相對復雜的表達式作為WHERE
子句對此實體框架 (EF6) 數據集執行計數操作,並期望它返回大約 100k 條記錄。
計數操作顯然是記錄被物化的地方,因此是最慢的操作。 在我們的生產環境中,計數操作大約需要 10 秒,這是不可接受的。
請注意,該操作是直接在 DbSet 上執行的(db 是 Context 類),因此不應發生延遲加載。
如何進一步優化此查詢以加快流程?
主要用例是顯示具有多個過濾條件的索引頁面,但 function 也用於根據服務類中的其他操作的需要將通用查詢寫入ParcelOrders
表,這可能是一個壞主意,導致非常復雜的查詢懶惰,可能會成為未來的問題。 該計數稍后用於分頁,實際顯示的記錄數(例如 500 條)要少得多。 這是一個使用 SQL 服務器的數據庫優先項目。
ParcelOrderSearchModel
是一個 C# 類,用於封裝查詢參數,僅由服務類使用,以便調用GetMatchingOrders
function。 請注意,在大多數調用中, ParcelOrderSearchModel
的大部分參數將為 null。
public List<ParcelOrderDto> GetMatchingOrders(ParcelOrderSearchModel searchModel)
{
// cryptic id known --> allow public access without login
if (String.IsNullOrEmpty(searchModel.KeyApplicationUserId) && searchModel.ExactKey_CrypticID == null)
throw new UnableToCheckPrivilegesException();
Func<ParcelOrder, bool> userPrivilegeValidation = (x => false);
if (searchModel.ExactKey_CrypticID != null)
{
userPrivilegeValidation = (x => true);
}
else if (searchModel.KeyApplicationUserId != null)
userPrivilegeValidation = privilegeService.UserPrivilegeValdationExpression(searchModel.KeyApplicationUserId);
var criteriaMatchValidation = CriteriaMatchValidationExpression(searchModel);
var parcelOrdersWithNoteHistoryPoints = db.HistoryPoint.Where(hp => hp.Type == (int)HistoryPointType.Note)
.Select(hp => hp.ParcelOrderID)
.Distinct();
Func<ParcelOrder, bool> completeExpression = order => userPrivilegeValidation(order) && criteriaMatchValidation(order);
searchModel.PaginationTotalCount = db.ParcelOrder.Count(completeExpression);
// todo: use this count for pagination
}
public Func<ParcelOrder, bool> CriteriaMatchValidationExpression(ParcelOrderSearchModel searchModel)
{
Func<ParcelOrder, bool> expression =
po => po.ID == 1;
expression =
po =>
(searchModel.KeyUploadID == null || po.UploadID == searchModel.KeyUploadID)
&& (searchModel.KeyCustomerID == null || po.CustomerID == searchModel.KeyCustomerID)
&& (searchModel.KeyContainingVendorProvidedId == null || (po.VendorProvidedID != null && searchModel.KeyContainingVendorProvidedId.Contains(po.VendorProvidedID)))
&& (searchModel.ExactKeyReferenceNumber == null || (po.CustomerID + "-" + po.ReferenceNumber) == searchModel.ExactKeyReferenceNumber)
&& (searchModel.ExactKey_CrypticID == null || po.CrypticID == searchModel.ExactKey_CrypticID)
&& (searchModel.ContainsKey_ReferenceNumber == null || (po.CustomerID + "-" + po.ReferenceNumber).Contains(searchModel.ContainsKey_ReferenceNumber))
&& (searchModel.OrKey_Referencenumber_ConsignmentID == null ||
((po.CustomerID + "-" + po.ReferenceNumber).Contains(searchModel.OrKey_Referencenumber_ConsignmentID)
|| (po.VendorProvidedID != null && po.VendorProvidedID.Contains(searchModel.OrKey_Referencenumber_ConsignmentID))))
&& (searchModel.KeyClientName == null || po.Parcel.Name.ToUpper().Contains(searchModel.KeyClientName.ToUpper()))
&& (searchModel.KeyCountries == null || searchModel.KeyCountries.Contains(po.Parcel.City.Country))
&& (searchModel.KeyOrderStates == null || searchModel.KeyOrderStates.Contains(po.State.Value))
&& (searchModel.KeyFromDateRegisteredToOTS == null || po.DateRegisteredToOTS > searchModel.KeyFromDateRegisteredToOTS)
&& (searchModel.KeyToDateRegisteredToOTS == null || po.DateRegisteredToOTS < searchModel.KeyToDateRegisteredToOTS)
&& (searchModel.KeyFromDateDeliveredToVendor == null || po.DateRegisteredToVendor > searchModel.KeyFromDateDeliveredToVendor)
&& (searchModel.KeyToDateDeliveredToVendor == null || po.DateRegisteredToVendor < searchModel.KeyToDateDeliveredToVendor);
return expression;
}
public Func<ParcelOrder, bool> UserPrivilegeValdationExpression(string userId)
{
var roles = GetRolesForUser(userId);
Func<ParcelOrder, bool> expression =
po => po.ID == 1;
if (roles != null)
{
if (roles.Contains("ParcelAdministrator"))
expression =
po => true;
else if (roles.Contains("RegionalAdministrator"))
{
var user = db.AspNetUsers.First(u => u.Id == userId);
if (user.RegionalAdministrator != null)
{
expression =
po => po.HubID == user.RegionalAdministrator.HubID;
}
}
else if (roles.Contains("Customer"))
{
var customerID = db.AspNetUsers.First(u => u.Id == userId).CustomerID;
expression =
po => po.CustomerID == customerID;
}
else
{
expression =
po => false;
}
}
return expression;
}
如果您可以避免它,請不要計入分頁。 只需返回第一頁。 計數總是很昂貴,而且對用戶體驗的影響很小。
無論如何,您構建的動態搜索都是錯誤的。
您正在調用IEnumerable.Count(Func<ParcelOrder,bool>)
,這將強制客戶端評估您應該調用IQueryable.Count(Expression<Func<ParcelOrder,bool>>)
。 這里:
Func<ParcelOrder, bool> completeExpression = order => userPrivilegeValidation(order) && criteriaMatchValidation(order);
searchModel.PaginationTotalCount = db.ParcelOrder.Count(completeExpression);
但是在 EF 中有一個更簡單、更好的模式:只需有條件地將條件添加到您的 IQueryable。
例如,在您的 DbContext 上放置一個方法,如下所示:
public IQueryable<ParcelOrder> SearchParcels(ParcelOrderSearchModel searchModel)
{
var q = this.ParcelOrders();
if (searchModel.KeyUploadID != null)
{
q = q.Where( po => po.UploadID == searchModel.KeyUploadID );
}
if (searchModel.KeyCustomerID != null)
{
q = q.Where( po.CustomerID == searchModel.KeyCustomerID );
}
//. . .
return q;
}
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