dotnet/efcore · error · InvalidOperationException

The LINQ expression ' ' could not be translated. Either…

Error message

The LINQ expression '{expression}' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or 'ToListAsync'. See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.

What it means

Inside ShaperProcessingExpressionVisitor, GetProjectionIndex resolves a ProjectionBindingExpression to a SelectExpression projection index. If the binding has no ProjectionMember and a null Index, it cannot be remapped and the visitor throws CoreStrings.TranslationFailed with the printed expression — meaning the projection binding could not be tied to any Cosmos SQL projection.

Solutions

1. Simplify the query (remove computed projections, grouping, subqueries) to isolate the binding that fails.
2. Avoid custom expression-tree manipulation that creates ProjectionBindingExpression without a backing projection.
3. Report the minimal repro to the EF Cosmos provider if it reproduces on stock LINQ.

try { await query.ToListAsync(ct); }
catch (InvalidOperationException ex) when (ex.Message.Contains("could not be translated"))
{
    logger.LogWarning(ex, "Projection binding failed; simplifying query");
    // simplify projection and retry
}

When it happens

Trigger: A query whose shaper references a projection binding that the Cosmos SelectExpression never produced — usually a binding created by a relational-only translation step or by a hand-built ExpressionTree.

Common situations: Mixing relational query visitors with Cosmos queries, custom IQueryTranslationPostprocessors that introduce bindings, or hitting an EF provider gap where a binding is emitted but no matching projection exists.

Related errors

• Complex projections in subqueries are currently unsupported.
• The LINQ expression ' ' could not be translated. Either…
• Unhandled expression node type
• A FromSqlExpression has an invalid arguments expression type
• Bind property on structural type coming out of scalar…

AI-assisted analysis of dotnet/efcore@3a2006ef56 (2026-08-11). Data as JSON: /api/errors/d7dda301a6861292. Report an issue: GitHub.

Appendix: source

Thrown at src/EFCore.Cosmos/Query/Internal/CosmosShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.cs:1478

                if (_entityTypeMaterializerExpressionsMapping.TryGetValue(entityType, out var materializerExpressions))
                {
                    return materializerExpressions;
                }
            }
            while ((entityType = entityType.BaseType!) != null);

            throw new UnreachableException();
        }

        private ProjectionExpression GetProjection(ProjectionBindingExpression projectionBindingExpression)
            => ((SelectExpression)projectionBindingExpression.QueryExpression).Projection[GetProjectionIndex(projectionBindingExpression)];

        private int GetProjectionIndex(ProjectionBindingExpression projectionBindingExpression)
            => projectionBindingExpression.ProjectionMember != null
                ? ((SelectExpression)projectionBindingExpression.QueryExpression)
                .GetMappedProjection(projectionBindingExpression.ProjectionMember).GetConstantValue<int>()
                : (projectionBindingExpression.Index
                    ?? throw new InvalidOperationException(CoreStrings.TranslationFailed(projectionBindingExpression.Print())));

        private NewExpression NewJsonReaderManager()
            => New(
                JsonReaderManagerConstructor, _jsonReaderDataParameter,
                MakeMemberAccess(QueryCompilationContext.QueryContextParameter, QueryContextQueryLoggerProperty));

        private static UnaryExpression ThrowInvalidToken(Expression tokenType, Type? type = null)
            => Throw(Call(CreateJsonReaderInvalidTokenTypeMethodInfo, tokenType), type ?? typeof(void));

        private ParameterExpression[] GetParametersForLambda(ITypeBase structuralType)
            => structuralType.TryGetOrdinalKey(out _)
                ? [QueryCompilationContext.QueryContextParameter, _jsonReaderDataParameter, _ownerKeySnapshotParameter, _ordinalParameter]
                : [QueryCompilationContext.QueryContextParameter, _jsonReaderDataParameter, _ownerKeySnapshotParameter];

        private bool IsTracking(ITypeBase structuralType, [NotNullWhen(true)] out IEntityType? entityType)
        {
            entityType = structuralType as IEntityType;
            return _queryStateManager && entityType != null && entityType.FindPrimaryKey() != null;

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