How to find min value in mongodb

You can use a combination of sort and limit to emulate min:

> db.foo.insert({a: 1})> db.foo.insert({a: 2})> db.foo.insert({a: 3})> db.foo.find().sort({a: 1}).limit(1) { "_id" : ObjectId("4df8d4a5957c623adae2ab7e"), "a" : 1 }

sort({a: 1}) is an ascending (minimum-first) sort on the a field, and we then only return the first document, which will be the minimum value for that field.

EDIT: note that this is written in the mongo shell, but you can do the same thing from C# or any other language using the appropriate driver methods.

The first

  db.sales.insert([    { "_id" : 1, "item" : "abc", "price" : 10, "quantity" : 2, "date" : ISODate("2014-01-01T08:00:00Z") },    { "_id" : 2, "item" : "jkl", "price" : 20, "quantity" : 1, "date" : ISODate("2014-02-03T09:00:00Z") },    { "_id" : 3, "item" : "xyz", "price" : 5, "quantity" : 5, "date" : ISODate("2014-02-03T09:05:00Z") },    { "_id" : 4, "item" : "abc", "price" : 10, "quantity" : 10, "date" : ISODate("2014-02-15T08:00:00Z") },    { "_id" : 5, "item" : "xyz", "price" : 5, "quantity" : 10, "date" : ISODate("2014-02-15T09:05:00Z") }  ])

The second, find the min value

  db.sales.aggregate(   [     {       $group:       {         _id: {},         minPrice: { $min: "$price" }       }     }   ]  );

result is

{ "_id" : {  }, "minPrice" : 5 }

You can also use min function like this.

 db.sales.aggregate(    [      {        $group:        {          _id: "$item",          minQuantity: { $min: "$quantity" }        }      }    ]  )

result are

{ "_id" : "xyz", "minQuantity" : 5 }{ "_id" : "jkl", "minQuantity" : 1 }{ "_id" : "abc", "minQuantity" : 2 }

$min is an accumulator operator available only in the $group stage.

UPDATE:Changed in version 3.2: $min is available in the $group and $project stages. In previous versions of MongoDB, $min is available in the $group stage only.

click here for more help

Just want to show how it can be done with official c# driver (since question about mongodb csharp) with one improvement: I am loading only one field, but not entire document if i want just find Min value of that field. Here is complete test case:

[TestMethod]public void Test(){  var _mongoServer = MongoServer.Create("mongodb://localhost:27020");  var database = _mongoServer.GetDatabase("StackoverflowExamples");  var col = database.GetCollection("items");  //Add test data  col.Insert(new Item() { IntValue = 1, SomeOtherField = "Test" });  col.Insert(new Item() { IntValue = 2 });  col.Insert(new Item() { IntValue = 3 });  col.Insert(new Item() { IntValue = 4 });  var item = col.FindAs<Item>(Query.And())  .SetSortOrder(SortBy.Ascending("IntValue"))  .SetLimit(1)  .SetFields("IntValue") //here i loading only field that i need  .Single();  var minValue = item.IntValue;  //Check that we found min value of IntValue field  Assert.AreEqual(1, minValue);  //Check that other fields are null in the document  Assert.IsNull(item.SomeOtherField);  col.RemoveAll();} 

And Item class :

public class Item{   public Item()   {     Id = ObjectId.GenerateNewId();   }    [BsonId]    public ObjectId Id { get; set; }    public int IntValue { get; set; }    public string SomeOtherField { get; set; }}

Update: Always trying to move further, so, here is extention method for finding min value within collection:

public static class MongodbExtentions{    public static int FindMinValue(this MongoCollection collection, string fieldName)    {        var cursor = collection.FindAs<BsonDocument>(Query.And())                     .SetSortOrder(SortBy.Ascending(fieldName))                     .SetLimit(1)                     .SetFields(fieldName);        var totalItemsCount = cursor.Count();        if (totalItemsCount == 0)            throw new Exception("Collection is empty");        var item = cursor.Single();        if (!item.Contains(fieldName))            throw new Exception(String.Format("Field '{0}' can't be find within '{1}' collection", fieldName, collection.Name));        return item.GetValue(fieldName).AsInt32; // here we can also check for if it can be parsed    }}

So above test case with this extention method can be rewrited like this:

[TestMethod]public void Test(){  var _mongoServer = MongoServer.Create("mongodb://localhost:27020");  var database = _mongoServer.GetDatabase("StackoverflowExamples");  var col = database.GetCollection("items");  var minValue = col.FindMinValue("IntValue");  Assert.AreEqual(1, minValue);  col.RemoveAll();}

Hope someone will use it ;).