MongoDb return filtered array elements out of one document in C#-CodePudding

I would like to filter specific array elements out of a single document.

My goal is returning a "CustomEntity" object only including arrays in "CustomLog.Logs" where LogEntity.Data is "System.string"

public class CustomEntity
{
    [BsonId]
    public string Id { get; set; }
    public LogEntity[] Logs { get; set; }
}

public class LogEntity
{
    public string Data { get; set; }
    public string DataType { get; set; }
}

My attempt:

Builders<CustomEntity>.Filter.ElemMatch(x => x.Logs,
Builders<LogEntity>.Filter.Eq(y => y.Data.DataType, "System.string"))

I tried to create some projections, but they just returned one array element (and i havnt got the code anymore..)

Any ideas?

CodePudding user response：

Issue & Concern

From this line:

Builders<LogEntity>.Filter.Eq(y => y.Data.DataType, "System.string")

This is incorrect as the Data is a string and doesn't contain the field definition of DataType.

Your filter query should be as below:

FilterDefinition<CustomEntity> filter = Builders<CustomEntity>.Filter.ElemMatch(x => x.Logs,
    Builders<LogEntity>.Filter.Eq(y => y.DataType, "System.string"));

Solution

To filter the matched element(s) in the array, you need the