$eq¶

Comparison Order比较顺序¶

For comparison of different BSON type values, see the specified BSON comparison order.有关不同BSON类型值的比较，请参阅指定的BSON比较顺序。

Match a Document Value匹配文档值¶

If the specified <value> is a document, the order of the fields in the document matters.如果指定了<value>是一个文档，文档中字段的顺序很重要。

Match an Array Value匹配数组值¶

If the specified <value> is an array, MongoDB matches documents where the <field> matches the array exactly or the <field> contains an element that matches the array exactly. 如果指定了<value>是一个数组，MongoDB匹配<field>完全匹配数组或<field>包含与数组完全匹配的元素。The order of the elements matters. 元素的顺序很重要。For an example, see Equals an Array Value.有关示例，请参阅等于数组值。

Match a Regular Expression匹配正则表达式¶

The expression { field: <value> } implicitly specifies a match on <value>. 表达式{ field: <value> }隐式指定了对<value>的匹配。MongoDB translates the implicit match to a more explicit form.MongoDB将隐式匹配转换为更显式的形式。

When the <value> is fixed, like a particular string, the expression is equivalent to using the $eq operator { field: { $eq: <value> } }.当<value>是固定的，就像特定字符串一样，表达式相当于使用$eq运算符{ field: { $eq: <value> } }。

If <value> is a regular expression, the statement is expanded using the $regex operator { field: { $regex: <value> } }.如果<value>是一个正则表达式，该语句使用$regex运算符{ field: { $regex: <value> } }展开。

For examples illustrating this behaviour, see Regex Match Behaviour.有关说明此行为的示例，请参阅正则表达式匹配行为。

Security Implications安全影响¶

Always use the explicit form { field: { $eq: <value> } } with user-supplied input to avoid problems with maliciously formed queries.始终对用户提供的输入使用显式形式{ field: { $eq: <value> } }，以避免恶意形成的查询出现问题。

Equals a Specified Value等于指定的值¶

The following example queries the inventory collection to select all documents where the value of the qty field equals 20:以下示例查询inventory集合以选择qty字段值等于20的所有文档：

db.inventory.find( { qty: { $eq: 20 } } )

The query is equivalent to:该查询相当于：

db.inventory.find( { qty: 20 } )

Both queries match the following documents:两个查询都匹配以下文档：

{ _id: 2, item: { name: "cd", code: "123" }, qty: 20, tags: [ "B" ] }
{ _id: 5, item: { name: "mn", code: "000" }, qty: 20, tags: [ [ "A", "B" ], "C" ] }

Field in Embedded Document Equals a Value嵌入文档中的字段等于一个值¶

The following example queries the inventory collection to select all documents where the value of the name field in the item document equals "ab". 以下示例查询inventory集合以选择item文档中name字段的值等于"ab"的所有文档。To specify a condition on a field in an embedded document, use the dot notation.要指定嵌入文档中字段的条件，请使用点表示法。

db.inventory.find( { "item.name": { $eq: "ab" } } )

The query is equivalent to:该查询相当于：

db.inventory.find( { "item.name": "ab" } )

Both queries match the following document:两个查询都匹配以下文档：

{ _id: 1, item: { name: "ab", code: "123" }, qty: 15, tags: [ "A", "B", "C" ] }

Array Element Equals a Value数组元素等于一个值¶

The following example queries the inventory collection to select all documents where the tags array contains an element with the value "B" [1]:以下示例查询inventory集合以选择tags数组包含值为"B"[1]的元素的所有文档：

db.inventory.find( { tags: { $eq: "B" } } )

The query is equivalent to:该查询相当于：

db.inventory.find( { tags: "B" } )

Both queries match the following documents:两个查询都匹配以下文档：

{ _id: 1, item: { name: "ab", code: "123" }, qty: 15, tags: [ "A", "B", "C" ] }
{ _id: 2, item: { name: "cd", code: "123" }, qty: 20, tags: [ "B" ] }
{ _id: 3, item: { name: "ij", code: "456" }, qty: 25, tags: [ "A", "B" ] }
{ _id: 4, item: { name: "xy", code: "456" }, qty: 30, tags: [ "B", "A" ] }

Equals an Array Value¶

The following example queries the inventory collection to select all documents where the tags array equals exactly the specified array or the tags array contains an element that equals the array [ "A", "B" ].以下示例查询inventory集合以选择tags数组正好等于指定数组或tags数组包含等于数组[ "A", "B" ]的元素的所有文档。

db.inventory.find( { tags: { $eq: [ "A", "B" ] } } )

The query is equivalent to:该查询相当于：

db.inventory.find( { tags: [ "A", "B" ] } )

Both queries match the following documents:两个查询都匹配以下文档：

{ _id: 3, item: { name: "ij", code: "456" }, qty: 25, tags: [ "A", "B" ] }
{ _id: 5, item: { name: "mn", code: "000" }, qty: 20, tags: [ [ "A", "B" ], "C" ] }

Regex Match Behaviour正则表达式匹配行为¶

The following examples demonstrate the differences in behavior between implicit and explict regular expression matching. 下面的示例演示了隐式和显式正则表达式匹配之间的行为差异。Consider a collection with these documents:考虑这些文件的集合：

{ _id: 001, company: "MongoDB" }
{ _id: 002, company: "MongoDB2" }

$eq match on a string在字符串上匹配

A string expands to return the same values whether an implicit match or an explicit use of $eq. 无论是隐式匹配还是显式使用$eq，字符串都会展开以返回相同的值。Both of these queries:这两个查询：

db.collection.find( { company: "MongoDB" }, {_id: 0 })
db.collection.find( { company: { $eq: "MongoDB" } }, {_id: 0 } )

return the following result:返回以下结果：

{ "company" : "MongoDB" }

$eq match on a regular expression在正则表达式上的匹配

An explicit query using $eq and a regular expression will only match an object which is also a regular expresssion. 使用$eq和正则表达式的显式查询将只匹配也是正则表达式的对象。The example query won’t return anything since values in the company field are strings.示例查询不会返回任何内容，因为company字段中的值是字符串。

db.collection.find( { company: { $eq: /MongoDB/ } }, {_id: 0 } )

Regular expression matches正则表达式匹配

A query with an implicit match against a regular expression is equivalent to a making a query with the $regex operator. 对正则表达式进行隐式匹配的查询相当于使用$regex运算符进行查询。Both of these queries:这两个查询：

db.collection.find( { company: /MongoDB/ }, {_id: 0 })
db.collection.find( { company: { $regex: /MongoDB/ } }, {_id: 0 } )

return the same results:返回相同的结果：

{ "company" : "MongoDB" }
{ "company" : "MongoDB2" }