C# 完整 Code
根據該筆記 [EFCore] LogTo 輸出 Linq 產生的 TSQL 語法，藉此來觀察是否發生資料庫存取，而輸出結果會稍微整理，以方便閱讀為主
using EFCoreCache.Models;
using Microsoft.EntityFrameworkCore;
namespace EFCoreCache
{
internal class Program
{
static void Main(string[] args)
{
AdventureWorks2022DbContext dbContext = new();
Console.WriteLine("----- Query1：第一次存取 Entity");
Console.WriteLine($"存取前 Person Entity Cache Count：{dbContext.Person.Local.Count}");
var query1 = dbContext.Person.SingleOrDefault(p => p.BusinessEntityID == 1);
Console.WriteLine($"存取後 Person Entity Cache Count：{dbContext.Person.Local.Count}");
Print(query1);
Console.WriteLine("----- Query2：理解 Cache 行為");
// 修正 Cache 內資料
query1.LastName = "LastNameFromCache";
// 直接更新資料庫內資料
dbContext.Person
.Where(w => w.BusinessEntityID == 1)
.ExecuteUpdate(e =>
e.SetProperty(sod => sod.LastName, "LastNameFromDB"));
var query2 = dbContext.Person.SingleOrDefault(p => p.BusinessEntityID == 1);
Print(query2);
Console.WriteLine("----- Query3：AsNoTracking()");
var query3 = dbContext.Person.AsNoTracking().SingleOrDefault(p => p.BusinessEntityID == 1);
Print(query3);
Console.WriteLine("----- Query4：Find()");
var query4 = dbContext.Person.Find(1);
Print(query4);
}
private static void Print(Person p)
{
Console.WriteLine($"內容輸出：{p.LastName}");
}
}
}後續會分別解釋每個 Query
Query1：第一次存取 Entity
Console.WriteLine($"存取前 Person Entity Cache Count：{dbContext.Person.Local.Count}");
var query1 = dbContext.Person.SingleOrDefault(p => p.BusinessEntityID == 1);
Console.WriteLine($"存取後 Person Entity Cache Count：{dbContext.Person.Local.Count}");
Print(query1);
存取前 Person Entity Cache Count：0
SELECT TOP(2) * FROM [Person].[Person] AS [p] WHERE [p].[BusinessEntityID] = 1
存取後 Person Entity Cache Count：1
內容輸出：Sanchez
Query2：理解 Cache 行為
更新 Query1 產生的 entity 資料，同時也更新資料庫內資料，藉此觀察使用 Single() 存取相同 entity 行為
// 修正 Cache 內資料
query1.LastName = "LastNameFromCache";
// 直接更新資料庫內資料
dbContext.Person
.Where(w => w.BusinessEntityID == 1)
.ExecuteUpdate(e =>
e.SetProperty(p => p.LastName, "LastNameFromDB"));
var query2 = dbContext.Person.SingleOrDefault(p => p.BusinessEntityID == 1);
Print(query2);
Queries are always executed against the database even if the entities returned in the result already exist in the context.
How Queries Work - The life of a query
3. For each item in the result set
a. If the query is a tracking query, EF checks if the data represents an entity already in the change tracker for the context instance
- If so, the existing entity is returned
- If not, a new entity is created, change tracking is set up, and the new entity is returned
b.If the query is a no-tracking query, then a new entity is always created and returned
另外 ExecuteUpdate 是不會有 cache 的，詳見 [EFCore] ExecuteUpdate 和 ExecuteDelete
UPDATE Person.Person SET LastName = 'LastNameFromDB' WHERE BusinessEntityID = 1
SELECT TOP(2) * FROM [Person].[Person] AS [p] WHERE [p].[BusinessEntityID] = 1
內容輸出：LastNameFromCache
使用 AsNoTracking() 就可以跳過 cache，直接存取資料庫並回傳
var query3 = dbContext.Person.AsNoTracking().SingleOrDefault(p => p.BusinessEntityID == 1);
Print(query3);
SELECT TOP(2) * FROM [Person].[Person] AS [p] WHERE [p].[BusinessEntityID] = 1
內容輸出：LastNameFromDB
Query4：Find()
當 cache 內有該 entity 時，使用 Find() 會直接回傳 cache 內 entity，不會有資料庫存取行為，沒有 TSQL 輸出，但 cache 內沒有該 entity 的話，才會去資料庫存取
var query4 = dbContext.Person.Find(1);
Print(query4);內容輸出：LastNameFromCache以上範例雖然是以 EFCore 9 為記錄內容，但在 EF 6.5.1 也是相同行為
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