EFCore：運算式樹-GroupJoin動態轉換為SelectMany

我想轉換以下查詢：

(from documentType in entitySet
 join userGroupId in Repository.ConvertToBigIntTable(userGroupIds, "userGroupId")
      on documentType.Id equals userGroupId.Id into UserGroupIds
 from userGroupId in UserGroupIds.DefaultIfEmpty()
 join documentTypePermission in Repository.DocumentTypePermissions
      on documentType.Id equals documentTypePermission.DocumentTypeId
 join userSelectionParam in Repository.UserSelectionParams
      on documentTypePermission.UserSelectionId equals userSelectionParam.Id
 where documentTypePermission.IsActive && 
       ((userSelectionParam.UserGroupId != null && userGroupId.Id != null)
        || (userSelectionParam.UserId != null && userSelectionParam.UserId == CurrentUserId))
 select documentTypePermission);

像這樣：

var query = 
    from documentType in entitySet
    from userGroupId in Repository.ConvertToBigIntTable(userGroupIds, "userGroupId")
        .Where(userGroupId => documentType.Id == userGroupId.Id)
        .DefaultIfEmpty()
    join documentTypePermission in Repository.DocumentTypePermissions
        on documentType.Id equals documentTypePermission.DocumentTypeId
    join userSelectionParam in Repository.UserSelectionParams
        on documentTypePermission.UserSelectionId equals userSelectionParam.Id

    ....

筆記：

1. 我已經準備好使用攔截運算式樹評估的設定QueryTranslationPreprocessor

2. 我需要使用第一個 linq 生成輸出等的邏輯.Call，.SelectMany然后將其轉換為上面顯示的第二個 linq 查詢

3. 需要注意的是，運算式引擎在內部生成了如此多的匿名型別，以至于我無法撰寫一個通用代碼來滿足具有此類 groupjoins 的 linq 的不同情況

這樣做的原因：

1. GroupJoin社區尚未準備好解決 EF Core 6 中的幾種問題

2. 我不能直接對 Linq 查詢進行更改，因為它們有 1000 個并且在幾個地方

uj5u.com熱心網友回復：

因此，在評估多個選項之后，執行上述操作的最佳方法如下所示 VisitMethodCall(MethodCallExpression node)

        if (node.Method.DeclaringType == typeof(Queryable) && node.Method.Name == nameof(Queryable.GroupJoin) && node.Arguments.Count == 5)
        {
            var outer = Visit(node.Arguments[0]);
            var inner = Visit(node.Arguments[1]);
            var outerKeySelector = Visit(node.Arguments[2]).UnwrapLambdaFromQuote();
            var innerKeySelector = Visit(node.Arguments[3]).UnwrapLambdaFromQuote();
            var resultSelector = Visit(node.Arguments[4]).UnwrapLambdaFromQuote();

            var outerKey = outerKeySelector.Body.ReplaceParameter(outerKeySelector.Parameters[0], resultSelector.Parameters[0]);
            var innerKey = innerKeySelector.Body;
            var keyMatch = MatchKeys(outerKey, innerKey);

            var innerQuery = Expression.Call(
                typeof(Queryable), nameof(Queryable.Where), new[] { innerKeySelector.Parameters[0].Type },
                inner, Expression.Lambda(keyMatch, innerKeySelector.Parameters));

            var asEnumerableInnerQuery = Expression.Call(
                            typeof(Enumerable),
                            nameof(Enumerable.AsEnumerable),
                            new Type[] { innerKeySelector.Parameters[0].Type }, innerQuery);

            var resultTypes = resultSelector.Parameters.Select(p => p.Type).ToArray();
            var tempProjectionType = typeof(Tuple<,>).MakeGenericType(resultTypes);
            var tempProjection = Expression.New(
                tempProjectionType.GetConstructor(resultTypes),
                new Expression[] { resultSelector.Parameters[0], asEnumerableInnerQuery },
                tempProjectionType.GetProperty("Item1"), tempProjectionType.GetProperty("Item2"));

            var tempQuery = Expression.Call(
                typeof(Queryable), nameof(Queryable.Select), new[] { outerKeySelector.Parameters[0].Type, tempProjectionType },
                outer, Expression.Lambda(tempProjection, resultSelector.Parameters[0]));

            var tempResult = Expression.Parameter(tempProjectionType, "p");
            var projection = resultSelector.Body
                .ReplaceParameter(resultSelector.Parameters[0], Expression.Property(tempResult, "Item1"))
                .ReplaceParameter(resultSelector.Parameters[1], Expression.Property(tempResult, "Item2"));

            var query = Expression.Call(
                typeof(Queryable), nameof(Queryable.Select), new[] { tempProjectionType, projection.Type },
                tempQuery, Expression.Lambda(projection, tempResult));
            return query;
        }
        return base.VisitMethodCall(node);
    }

標籤：林克 实体框架核心 链接到实体 表达式树 ef-core-6.0

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