MongoDB-记录查询

该页提供了基于MongoDB C# Driver. 查询操作方法MongoCollection.Find() 演示，示例代码中查询inventory集合，以下代码先写入记录：

var documents = new BsonDocument[]
{
    new BsonDocument
    {
        { "item", "journal" },
        { "qty", 25 },
        { "size", new BsonDocument { { "h", 14 }, { "w", 21 }, {  "uom", "cm"} } },
        { "status", "A" }
    },
    new BsonDocument
    {
        { "item", "notebook" },
        { "qty", 50 },
        { "size", new BsonDocument { { "h",  8.5 }, { "w", 11 }, {  "uom", "in"} } },
        { "status", "A" }
    },
    new BsonDocument
    {
        { "item", "paper" },
        { "qty", 100 },
        { "size", new BsonDocument { { "h",  8.5 }, { "w", 11 }, {  "uom", "in"} } },
        { "status", "D" }
    },
    new BsonDocument
    {
        { "item", "planner" },
        { "qty", 75 },
        { "size", new BsonDocument { { "h", 22.85 }, { "w", 30  }, {  "uom", "cm"} } },
        { "status", "D" }
    },
    new BsonDocument
    {
        { "item", "postcard" },
        { "qty", 45 },
        { "size", new BsonDocument { { "h", 10 }, { "w", 15.25 }, {  "uom", "cm"} } },
        { "status", "A" }
    },
};
collection.InsertMany(documents);

查询集合中的全部文档

若要选择集合中的所有文档，请将空文档作为查询筛选器参数传递给find方法。查询筛选器参数确定选择标准：

var filter = Builders<BsonDocument>.Filter.Empty;
var result = collection.Find(filter).ToList();

此操作对应于以下SQL语句：

SELECT * FROM inventory

指定相等条件

指定相等条件，使用Eq方法构建一个过滤器

Builders<BsonDocument>.Filter.Eq(<field>, <value>);

以下示例查询 inventory集合的全部文档，条件是 status="D":

var filter = Builders<BsonDocument>.Filter.Eq("status", "D");
var result = collection.Find(filter).ToList();

此操作对应于以下SQL语句：

SELECT * FROM inventory WHERE status = "D"

使用查询操作符指定条件

除了相等过滤器，MongoDB还提供了多种查询操作符来生成过滤器，以下示例使用 FilterDefinitionBuilder 方法创建文档的过滤器:

var builder = Builders<BsonDocument>.Filter;
builder.And(builder.Eq(<field1>, <value1>), builder.Lt(<field2>, <value2>));

The following example retrieves all documents from the inventory collection where status equals either "A" or "D":

var filter = Builders<BsonDocument>.Filter.In("status", new[] { "A", "D" });
var result = collection.Find(filter).ToList();

NOTE

Although you can express this query using the $or operator, use the $in operator rather than the $oroperator when performing equality checks on the same field.

The operation corresponds to the following SQL statement:

SELECT * FROM inventory WHERE status in ("A", "D")

Refer to the Query and Projection Operators document for the complete list of MongoDB query operators.

Specify AND Conditions

A compound query can specify conditions for more than one field in the collection’s documents. Implicitly, a logical AND conjunction connects the clauses of a compound query so that the query selects the documents in the collection that match all the conditions.

The following example retrieves all documents in the inventory collection where the status equals "A" andqty is less than ($lt) 30:

var builder = Builders<BsonDocument>.Filter;
var filter = builder.And(builder.Eq("status", "A"), builder.Lt("qty", 30));
var result = collection.Find(filter).ToList();

The operation corresponds to the following SQL statement:

SELECT * FROM inventory WHERE status = "A" AND qty < 30

See comparison operators for other MongoDB comparison operators.

Specify OR Conditions

Using the $or operator, you can specify a compound query that joins each clause with a logical OR conjunction so that the query selects the documents in the collection that match at least one condition.

The following example retrieves all documents in the collection where the status equals "A" or qty is less than ($lt) 30:

var builder = Builders<BsonDocument>.Filter;
var filter = builder.Or(builder.Eq("status", "A"), builder.Lt("qty", 30));
var result = collection.Find(filter).ToList();

The operation corresponds to the following SQL statement:

SELECT * FROM inventory WHERE status = "A" OR qty < 30

NOTE

Queries which use comparison operators are subject to Type Bracketing.

Specify AND as well as OR Conditions

In the following example, the compound query document selects all documents in the collection where the status equals "A" and either qty is less than ($lt) 30 or item starts with the character p:

var builder = Builders<BsonDocument>.Filter;
var filter = builder.And(
    builder.Eq("status", "A"),
    builder.Or(builder.Lt("qty", 30), builder.Regex("item", new BsonRegularExpression("^p"))));
var result = collection.Find(filter).ToList();

The operation corresponds to the following SQL statement:

SELECT * FROM inventory WHERE status = "A" AND ( qty < 30 OR item LIKE "p%")

NOTE

MongoDB supports regular expressions $regex queries to perform string pattern matches.