如何将指定Elasticsearch DSL查询转换为C# NEST查询？

Got it, let's convert that Elasticsearch DSL query to NEST C# code for you. Here's how you can replicate exactly what your DSL does:

First, a quick recap of what your original query accomplishes:

• Sets size: 0 to avoid returning individual documents (we only care about aggregation results)
• Filters results to only include documents where projectId.keyword is in the list ["1", "2", "18"]
• Groups those filtered documents by projectId.keyword
• For each project group, calculates the latest processedAt timestamp using a max aggregation

Here's the matching NEST code:

// Assuming you have an ElasticClient instance named "client"
// Replace YourDocumentType with your actual POCO that maps to your Elasticsearch docs
var searchResponse = await client.SearchAsync<YourDocumentType>(s => s
    .Index("project")
    .Size(0) // Skip returning individual documents
    .Aggregations(a => a
        // First filter aggregation to narrow down to specific project IDs
        .Filter("group_by_projectId", filter => filter
            .Filter(f => f
                .Terms(t => t
                    .Field(p => p.ProjectId.Suffix("keyword"))
                    .Terms(new[] { "1", "2", "18" })
                )
            )
            // Nested aggregations inside the filter
            .Aggregations(nestedAggs => nestedAggs
                .Terms("project_tags", terms => terms
                    .Field(p => p.ProjectId.Suffix("keyword"))
                    .Size(100)
                    // Max aggregation to get the latest processed time per project
                    .Aggregations(maxAgg => maxAgg
                        .Max("last_process_time", m => m
                            .Field(p => p.ProcessedAt)
                        )
                    )
                )
            )
        )
    )
);

Quick Notes: #

• Suffix("keyword") ensures we target the keyword sub-field of projectId, just like your original DSL.
• If you're using a synchronous client, replace SearchAsync with Search.
• Make sure your POCO (YourDocumentType) has properties ProjectId and ProcessedAt that map correctly to your Elasticsearch fields.

To access the aggregation results after running the query, you can use this snippet:

// Extract the filter aggregation
var filterAggregation = searchResponse.Aggregations.Filter("group_by_projectId");
// Extract the terms aggregation inside the filter
var projectTermsAgg = filterAggregation.Terms("project_tags");

// Iterate through each project bucket
foreach (var projectBucket in projectTermsAgg.Buckets)
{
    string projectId = projectBucket.Key;
    DateTime? latestProcessTime = projectBucket.Max("last_process_time")?.Value;
    
    // Use the results as needed
    Console.WriteLine($"Project {projectId} latest process time: {latestProcessTime}");
}

Content of the question originates from Stack Exchange, asked by Mikail